Internet DRAFT - draft-wang-avt-rfc3984bis

draft-wang-avt-rfc3984bis



Audio/Video Transport WG                                     Y.-K. Wang 
Internet Draft                                                S. Wenger 
Intended status: Standards track                         M.M. Hanuksela 
Expires: January 2009                                             Nokia 
                                                         T. Stockhammer 
                                                         Nomor Research 
                                                          M. Westerlund 
                                                               Ericsson 
                                                              D. Singer 
                                                                  Apple 
                                                          July 14, 2008 
                                    
 
 
                                      
                    RTP Payload Format for H.264 Video 
                     draft-wang-avt-rfc3984bis-01.txt 


Status of this Memo 

   By submitting this Internet-Draft, each author represents that any 
   applicable patent or other IPR claims of which he or she is aware 
   have been or will be disclosed, and any of which he or she becomes 
   aware will be disclosed, in accordance with Section 6 of BCP 79. 

   Internet-Drafts are working documents of the Internet Engineering 
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   This Internet-Draft will expire on January 14, 2009. 

Copyright Notice 

   Copyright (C) The IETF Trust (2008). 

 
 
 
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Abstract 

   This memo describes an RTP Payload format for the ITU-T 
   Recommendation H.264 video codec and the technically identical 
   ISO/IEC International Standard 14496-10 video codec.  The RTP payload 
   format allows for packetization of one or more Network Abstraction 
   Layer Units (NALUs), produced by an H.264 video encoder, in each RTP 
   payload.  The payload format has wide applicability, as it supports 
   applications from simple low bit-rate conversational usage, to 
   Internet video streaming with interleaved transmission, to high bit-
   rate video-on-demand. 

   This memo intends to obsolete RFC 3984. 

    

Table of Contents 

    
   1. Introduction...................................................4 
      1.1. The H.264 Codec...........................................4 
      1.2. Parameter Set Concept.....................................5 
      1.3. Network Abstraction Layer Unit Types......................6 
   2. Conventions....................................................7 
   3. Scope..........................................................7 
   4. Definitions and Abbreviations..................................7 
      4.1. Definitions...............................................7 
      4.2. Abbreviations.............................................9 
   5. RTP Payload Format.............................................9 
      5.1. RTP Header Usage..........................................9 
      5.2. Common Structure of the RTP Payload Format...............12 
      5.3. NAL Unit Octet Usage.....................................13 
      5.4. Packetization Modes......................................15 
      5.5. Decoding Order Number (DON)..............................16 
      5.6. Single NAL Unit Packet...................................19 
      5.7. Aggregation Packets......................................20 
         5.7.1. Single-Time Aggregation Packet......................22 
         5.7.2. Multi-Time Aggregation Packets (MTAPs)..............24 
         5.7.3. Fragmentation Units (FUs)...........................28 
   6. Packetization Rules...........................................32 
      6.1. Common Packetization Rules...............................32 
      6.2. Single NAL Unit Mode.....................................33 
      6.3. Non-Interleaved Mode.....................................33 
      6.4. Interleaved Mode.........................................33 
   7. De-Packetization Process......................................34 
      7.1. Single NAL Unit and Non-Interleaved Mode.................34 
      7.2. Interleaved Mode.........................................34 
 
 
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         7.2.1. Size of the Deinterleaving Buffer...................35 
         7.2.2. Deinterleaving Process..............................35 
      7.3. Additional De-Packetization Guidelines...................37 
   8. Payload Format Parameters.....................................38 
      8.1. MIME Registration........................................38 
      8.2. SDP Parameters...........................................50 
         8.2.1. Mapping of MIME Parameters to SDP...................50 
         8.2.2. Usage with the SDP Offer/Answer Model...............50 
         8.2.3. Usage in Declarative Session Descriptions...........55 
      8.3. Examples.................................................56 
      8.4. Parameter Set Considerations.............................61 
   9. Security Considerations.......................................63 
   10. Congestion Control...........................................64 
   11. IANA Consideration...........................................65 
   12. Informative Appendix: Application Examples...................65 
      12.1. Video Telephony according to ITU-T Recommendation H.241 
      Annex A.......................................................65 
      12.2. Video Telephony, No Slice Data Partitioning, No NAL Unit 
      Aggregation...................................................65 
      12.3. Video Telephony, Interleaved Packetization Using NAL Unit 
      Aggregation...................................................66 
      12.4. Video Telephony with Data Partitioning..................66 
      12.5. Video Telephony or Streaming with FUs and Forward Error 
      Correction....................................................67 
      12.6. Low Bit-Rate Streaming..................................69 
      12.7. Robust Packet Scheduling in Video Streaming.............70 
   13. Informative Appendix: Rationale for Decoding Order Number....71 
      13.1. Introduction............................................71 
      13.2. Example of Multi-Picture Slice Interleaving.............71 
      13.3. Example of Robust Packet Scheduling.....................73 
      13.4. Robust Transmission Scheduling of Redundant Coded Slices77 
      13.5. Remarks on Other Design Possibilities...................77 
   14. Acknowledgements.............................................78 
   15. References...................................................78 
      15.1. Normative References....................................78 
      15.2. Informative References..................................79 
   Authors' Addresses...............................................80 
   Intellectual Property Statement..................................82 
   Disclaimer of Validity...........................................82 
   Acknowledgement..................................................83 
   16. Backward compatibility to RFC 3984...........................83 
   17. Changes from RFC 3984........................................83 
      17.1. Technical changes.......................................83 
      17.2. Editorial changes.......................................86 
   18. Open issues..................................................97 
    

 
 
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1. Introduction 

   This memo intends to obsolete RFC 3984. 

1.1. The H.264 Codec 

   This memo specifies an RTP payload specification for the video coding 
   standard known as ITU-T Recommendation H.264 [1] and ISO/IEC 
   International Standard 14496 Part 10 [2] (both also known as Advanced 
   Video Coding, or AVC).  Recommendation H.264 was approved by ITU-T on 
   May 2003, and the approved draft specification is available for 
   public review [8].  In this memo the H.264 acronym is used for the 
   codec and the standard, but the memo is equally applicable to the 
   ISO/IEC counterpart of the coding standard. 

   The H.264 video codec has a very broad application range that covers 
   all forms of digital compressed video from, low bit-rate Internet 
   streaming applications to HDTV broadcast and Digital Cinema 
   applications with nearly lossless coding.  Compared to the current 
   state of technology, the overall performance of H.264 is such that 
   bit rate savings of 50% or more are reported.  Digital Satellite TV 
   quality, for example, was reported to be achievable at 1.5 Mbit/s, 
   compared to the current operation point of MPEG 2 video at around 3.5 
   Mbit/s [9]. 

   The codec specification [1] itself distinguishes conceptually between 
   a video coding layer (VCL) and a network abstraction layer (NAL).  
   The VCL contains the signal processing functionality of the codec; 
   mechanisms such as transform, quantization, and motion compensated 
   prediction; and a loop filter.  It follows the general concept of 
   most of today's video codecs, a macroblock-based coder that uses 
   inter picture prediction with motion compensation and transform 
   coding of the residual signal.  The VCL encoder outputs slices: a bit 
   string that contains the macroblock data of an integer number of 
   macroblocks, and the information of the slice header (containing the 
   spatial address of the first macroblock in the slice, the initial 
   quantization parameter, and similar information).  Macroblocks in 
   slices are arranged in scan order unless a different macroblock 
   allocation is specified, by using the so-called Flexible Macroblock 
   Ordering syntax.  In-picture prediction is used only within a slice.  
   More information is provided in [9]. 

   The Network Abstraction Layer (NAL) encoder encapsulates the slice 
   output of the VCL encoder into Network Abstraction Layer Units (NAL 
   units), which are suitable for transmission over packet networks or 
   use in packet oriented multiplex environments.  Annex B of H.264 
   defines an encapsulation process to transmit such NAL units over 
 
 
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   byte-stream oriented networks.  In the scope of this memo, Annex B is 
   not relevant. 

   Internally, the NAL uses NAL units.  A NAL unit consists of a one-
   byte header and the payload byte string.  The header indicates the 
   type of the NAL unit, the (potential) presence of bit errors or 
   syntax violations in the NAL unit payload, and information regarding 
   the relative importance of the NAL unit for the decoding process.  
   This RTP payload specification is designed to be unaware of the bit 
   string in the NAL unit payload. 

   One of the main properties of H.264 is the complete decoupling of the 
   transmission time, the decoding time, and the sampling or 
   presentation time of slices and pictures.  The decoding process 
   specified in H.264 is unaware of time, and the H.264 syntax does not 
   carry information such as the number of skipped frames (as is common 
   in the form of the Temporal Reference in earlier video compression 
   standards).  Also, there are NAL units that affect many pictures and 
   that are, therefore, inherently timeless.  For this reason, the 
   handling of the RTP timestamp requires some special considerations 
   for NAL units for which the sampling or presentation time is not 
   defined or, at transmission time, unknown. 

1.2. Parameter Set Concept 

   One very fundamental design concept of H.264 is to generate self-
   contained packets, to make mechanisms such as the header duplication 
   of RFC 2429 [10] or MPEG-4's Header Extension Code (HEC) [11] 
   unnecessary.  This was achieved by decoupling information relevant to 
   more than one slice from the media stream.  This higher layer meta 
   information should be sent reliably, asynchronously, and in advance 
   from the RTP packet stream that contains the slice packets. 
   (Provisions for sending this information in-band are also available 
   for applications that do not have an out-of-band transport channel 
   appropriate for the purpose.)  The combination of the higher-level 
   parameters is called a parameter set.  The H.264 specification 
   includes two types of parameter sets: sequence parameter set and 
   picture parameter set.  An active sequence parameter set remains 
   unchanged throughout a coded video sequence, and an active picture 
   parameter set remains unchanged within a coded picture.  The sequence 
   and picture parameter set structures contain information such as 
   picture size, optional coding modes employed, and macroblock to slice 
   group map. 

   To be able to change picture parameters (such as the picture size) 
   without having to transmit parameter set updates synchronously to the 
   slice packet stream, the encoder and decoder can maintain a list of 
 
 
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   more than one sequence and picture parameter set.  Each slice header 
   contains a codeword that indicates the sequence and picture parameter 
   set to be used. 

   This mechanism allows the decoupling of the transmission of parameter 
   sets from the packet stream, and the transmission of them by external 
   means (e.g., as a side effect of the capability exchange), or through 
   a (reliable or unreliable) control protocol.  It may even be possible 
   that they are never transmitted but are fixed by an application 
   design specification. 

1.3. Network Abstraction Layer Unit Types 

   Tutorial information on the NAL design can be found in [12], [13], 
   and [14]. 

   All NAL units consist of a single NAL unit type octet, which also co-
   serves as the payload header of this RTP payload format.  The payload 
   of a NAL unit follows immediately. 

   The syntax and semantics of the NAL unit type octet are specified in 
   [1], but the essential properties of the NAL unit type octet are 
   summarized below.  The NAL unit type octet has the following format: 

      +---------------+ 
      |0|1|2|3|4|5|6|7| 
      +-+-+-+-+-+-+-+-+ 
      |F|NRI|  Type   | 
      +---------------+ 
    
   The semantics of the components of the NAL unit type octet, as 
   specified in the H.264 specification, are described briefly below. 

   F: 1 bit 
      forbidden_zero_bit.  The H.264 specification declares a value of 
      1 as a syntax violation. 

   NRI: 2 bits 
      nal_ref_idc.  A value of 00 indicates that the content of the NAL 
      unit is not used to reconstruct reference pictures for inter 
      picture prediction.  Such NAL units can be discarded without 
      risking the integrity of the reference pictures.  Values greater 
      than 00 indicate that the decoding of the NAL unit is required to 
      maintain the integrity of the reference pictures. 

   Type: 5 bits 
      nal_unit_type.  This component specifies the NAL unit payload 
 
 
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      type as defined in table 7-1 of [1], and later within this memo.  
      For a reference of all currently defined NAL unit types and their 
      semantics, please refer to section 7.4.1 in [1]. 

   This memo introduces new NAL unit types, which are presented in 
   section 5.2.  The NAL unit types defined in this memo are marked as 
   unspecified in [1].  Moreover, this specification extends the 
   semantics of F and NRI as described in section 5.3. 

2. Conventions 

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", 
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this 
   document are to be interpreted as described in RFC-2119 [3]. 

   This specification uses the notion of setting and clearing a bit when 
   bit fields are handled.  Setting a bit is the same as assigning that 
   bit the value of 1 (On).  Clearing a bit is the same as assigning 
   that bit the value of 0 (Off). 

3. Scope 

   This payload specification can only be used to carry the "naked" 
   H.264 NAL unit stream over RTP, and not the bitstream format 
   discussed in Annex B of H.264.  Likely, the first applications of 
   this specification will be in the conversational multimedia field, 
   video telephony or video conferencing, but the payload format also 
   covers other applications, such as Internet streaming and TV over IP. 

4. Definitions and Abbreviations 

4.1. Definitions 

   This document uses the definitions of [1].  The following terms, 
   defined in [1], are summed up for convenience: 

      access unit: A set of NAL units always containing a primary coded 
      picture.  In addition to the primary coded picture, an access 
      unit may also contain one or more redundant coded pictures or 
      other NAL units not containing slices or slice data partitions of 
      a coded picture.  The decoding of an access unit always results 
      in a decoded picture. 

      coded video sequence: A sequence of access units that consists, 
      in decoding order, of an instantaneous decoding refresh (IDR) 
      access unit followed by zero or more non-IDR access units 

 
 
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      including all subsequent access units up to but not including any 
      subsequent IDR access unit. 

      IDR access unit: An access unit in which the primary coded 
      picture is an IDR picture. 

      IDR picture: A coded picture containing only slices with I or SI 
      slice types that causes a "reset" in the decoding process.  After 
      the decoding of an IDR picture, all following coded pictures in 
      decoding order can be decoded without inter prediction from any 
      picture decoded prior to the IDR picture. 

      primary coded picture: The coded representation of a picture to 
      be used by the decoding process for a bitstream conforming to 
      H.264.  The primary coded picture contains all macroblocks of the 
      picture. 

      redundant coded picture: A coded representation of a picture or a 
      part of a picture.  The content of a redundant coded picture 
      shall not be used by the decoding process for a bitstream 
      conforming to H.264.  The content of a redundant coded picture 
      may be used by the decoding process for a bitstream that contains 
      errors or losses. 

      VCL NAL unit: A collective term used to refer to coded slice and 
      coded data partition NAL units. 

   In addition, the following definitions apply: 

      decoding order number (DON): A field in the payload structure, or 
      a derived variable indicating NAL unit decoding order.  Values of 
      DON are in the range of 0 to 65535, inclusive.  After reaching 
      the maximum value, the value of DON wraps around to 0. 

      NAL unit decoding order: A NAL unit order that conforms to the 
      constraints on NAL unit order given in section 7.4.1.2 in [1]. 

      NALU-time: The value that the RTP timestamp would have if the NAL 
      unit would be transported in its own RTP packet. 

      transmission order: The order of packets in ascending RTP 
      sequence number order (in modulo arithmetic).  Within an 
      aggregation packet, the NAL unit transmission order is the same 
      as the order of appearance of NAL units in the packet. 

      media aware network element (MANE): A network element, such as a 
      middlebox or application layer gateway that is capable of parsing 
 
 
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      certain aspects of the RTP payload headers or the RTP payload and 
      reacting to the contents. 

         Informative note: The concept of a MANE goes beyond normal 
         routers or gateways in that a MANE has to be aware of the 
         signaling (e.g., to learn about the payload type mappings of 
         the media streams), and in that it has to be trusted when 
         working with SRTP.  The advantage of using MANEs is that they 
         allow packets to be dropped according to the needs of the 
         media coding.  For example, if a MANE has to drop packets due 
         to congestion on a certain link, it can identify those packets 
         whose dropping has the smallest negative impact on the user 
         experience and remove them in order to remove the congestion 
         and/or keep the delay low. 

4.2. Abbreviations 

      DON:        Decoding Order Number 
      DONB:       Decoding Order Number Base 
      DOND:       Decoding Order Number Difference 
      FEC:        Forward Error Correction 
      FU:         Fragmentation Unit 
      IDR:        Instantaneous Decoding Refresh 
      IEC:        International Electrotechnical Commission 
      ISO:        International Organization for Standardization 
      ITU-T:      International Telecommunication Union, 
                  Telecommunication Standardization Sector 
      MANE:       Media Aware Network Element 
      MTAP:       Multi-Time Aggregation Packet 
      MTAP16:     MTAP with 16-bit timestamp offset 
      MTAP24:     MTAP with 24-bit timestamp offset 
      NAL:        Network Abstraction Layer 
      NALU:       NAL Unit 
      SEI:        Supplemental Enhancement Information 
      STAP:       Single-Time Aggregation Packet 
      STAP-A:     STAP type A 
      STAP-B:     STAP type B 
      TS:         Timestamp 
      VCL:        Video Coding Layer 

5. RTP Payload Format 

5.1. RTP Header Usage 

   The format of the RTP header is specified in RFC 3550 [4] and 
   reprinted in Figure 1 for convenience.  This payload format uses the 
   fields of the header in a manner consistent with that specification. 
 
 
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   When one NAL unit is encapsulated per RTP packet, the RECOMMENDED RTP 
   payload format is specified in section 5.6.  The RTP payload (and the 
   settings for some RTP header bits) for aggregation packets and 
   fragmentation units are specified in sections 5.7 and 5.8, 
   respectively. 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |V=2|P|X|  CC   |M|     PT      |       sequence number         | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                           timestamp                           | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |           synchronization source (SSRC) identifier            | 
   +=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+=+ 
   |            contributing source (CSRC) identifiers             | 
   |                             ....                              | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
                 Figure 1 RTP header according to RFC 3550 

   The RTP header information to be set according to this RTP payload 
   format is set as follows: 

   Marker bit (M): 1 bit 
      Set for the very last packet of the access unit indicated by the 
      RTP timestamp, in line with the normal use of the M bit in video 
      formats, to allow an efficient playout buffer handling.  For 
      aggregation packets (STAP and MTAP), the marker bit in the RTP 
      header MUST be set to the value that the marker bit of the last 
      NAL unit of the aggregation packet would have been if it were 
      transported in its own RTP packet.  Decoders MAY use this bit as 
      an early indication of the last packet of an access unit, but 
      MUST NOT rely on this property. 

         Informative note: Only one M bit is associated with an 
         aggregation packet carrying multiple NAL units.  Thus, if a 
         gateway has re-packetized an aggregation packet into several 
         packets, it cannot reliably set the M bit of those packets. 

   Payload type (PT): 7 bits 
      The assignment of an RTP payload type for this new packet format 
      is outside the scope of this document and will not be specified 
      here.  The assignment of a payload type has to be performed 
      either through the profile used or in a dynamic way. 


 
 
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   Sequence number (SN): 16 bits 
      Set and used in accordance with RFC 3550.  For the single NALU 
      and non-interleaved packetization mode, the sequence number is 
      used to determine decoding order for the NALU. 

   Timestamp: 32 bits 
      The RTP timestamp is set to the sampling timestamp of the 
      content.  A 90 kHz clock rate MUST be used.  

      If the NAL unit has no timing properties of its own (e.g., 
      parameter set and SEI NAL units), the RTP timestamp is set to the 
      RTP timestamp of the primary coded picture of the access unit in 
      which the NAL unit is included, according to section 7.4.1.2 of 
      [1]. 

      The setting of the RTP Timestamp for MTAPs is defined in section 
      5.7.2. 

      Receivers SHOULD ignore any picture timing SEI messages included 
      in access units that have only one display timestamp.  Instead, 
      receivers SHOULD use the RTP timestamp for synchronizing the 
      display process. 

      RTP senders SHOULD NOT transmit picture timing SEI messages for 
      pictures that are not supposed to be displayed as multiple 
      fields. 

      If one access unit has more than one display timestamp carried in 
      a picture timing SEI message, then the information in the SEI 
      message SHOULD be treated as relative to the RTP timestamp, with 
      the earliest event occurring at the time given by the RTP 
      timestamp, and subsequent events later, as given by the 
      difference in SEI message picture timing values.  Let tSEI1, 
      tSEI2, ..., tSEIn be the display timestamps carried in the SEI 
      message of an access unit, where tSEI1 is the earliest of all 
      such timestamps.  Let tmadjst() be a function that adjusts the 
      SEI messages time scale to a 90-kHz time scale.  Let TS be the 
      RTP timestamp.  Then, the display time for the event associated 
      with tSEI1 is TS.  The display time for the event with tSEIx, 
      where x is [2..n] is TS + tmadjst (tSEIx - tSEI1). 

         Informative note: Displaying coded frames as fields is needed 
         commonly in an operation known as 3:2 pulldown, in which film 
         content that consists of coded frames is displayed on a 
         display using interlaced scanning.  The picture timing SEI 
         message enables carriage of multiple timestamps for the same 
         coded picture, and therefore the 3:2 pulldown process is 
 
 
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         perfectly controlled.  The picture timing SEI message 
         mechanism is necessary because only one timestamp per coded 
         frame can be conveyed in the RTP timestamp. 

         Informative note: Because H.264 allows the decoding order to 
         be different from the display order, values of RTP timestamps 
         may not be monotonically non-decreasing as a function of RTP 
         sequence numbers.  Furthermore, the value for interarrival 
         jitter reported in the RTCP reports may not be a trustworthy 
         indication of the network performance, as the calculation 
         rules for interarrival jitter (section 6.4.1 of RFC 3550) 
         assume that the RTP timestamp of a packet is directly 
         proportional to its transmission time. 

5.2. Common Structure of the RTP Payload Format 

   The payload format defines three different basic payload structures.  
   A receiver can identify the payload structure by the first byte of 
   the RTP payload, which co-serves as the RTP payload header and, in 
   some cases, as the first byte of the payload.  This byte is always 
   structured as a NAL unit header.  The NAL unit type field indicates 
   which structure is present.  The possible structures are as follows: 

   Single NAL Unit Packet: Contains only a single NAL unit in the 
   payload.  The NAL header type field will be equal to the original NAL 
   unit type; i.e., in the range of 1 to 23, inclusive.  Specified in 
   section 5.6. 

   Aggregation packet: Packet type used to aggregate multiple NAL units 
   into a single RTP payload.  This packet exists in four versions, the 
   Single-Time Aggregation Packet type A (STAP-A), the Single-Time 
   Aggregation Packet type B (STAP-B), Multi-Time Aggregation Packet 
   (MTAP) with 16-bit offset (MTAP16), and Multi-Time Aggregation Packet 
   (MTAP) with 24-bit offset (MTAP24).  The NAL unit type numbers 
   assigned for STAP-A, STAP-B, MTAP16, and MTAP24 are 24, 25, 26, and 
   27, respectively.  Specified in section 5.7. 

   Fragmentation unit: Used to fragment a single NAL unit over multiple 
   RTP packets.  Exists with two versions, FU-A and FU-B, identified 
   with the NAL unit type numbers 28 and 29, respectively.  Specified in 
   section 5.8. 

      Informative note: This specification does not limit the size of 
      NAL units encapsulated in single NAL unit packets and 
      fragmentation units.  The maximum size of a NAL unit encapsulated 
      in any aggregation packet is 65535 bytes. 

 
 
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   Table 1 summarizes NAL unit types and the corresponding RTP packet 
   types when each of these NAL units is directly used a packet payload, 
   and where the types are described in this memo.  

     Table 1.  Summary of NAL unit types and the corresponding packet 
                                   types  

      NAL Unit  Packet    Packet Type Name               Section 
      Type      Type 
      --------------------------------------------------------- 
      0        undefined                                    - 
      1-23     NAL unit  Single NAL unit packet             5.6 
      24       STAP-A    Single-time aggregation packet     5.7.1 
      25       STAP-B    Single-time aggregation packet     5.7.1 
      26       MTAP16    Multi-time aggregation packet      5.7.2 
      27       MTAP24    Multi-time aggregation packet      5.7.2 
      28       FU-A      Fragmentation unit                 5.8 
      29       FU-B      Fragmentation unit                 5.8 
      30-31    undefined                                    - 
    
5.3. NAL Unit Octet Usage 

   The structure and semantics of the NAL unit octet were introduced in 
   section 1.3.  For convenience, the format of the NAL unit type octet 
   is reprinted below: 

      +---------------+ 
      |0|1|2|3|4|5|6|7| 
      +-+-+-+-+-+-+-+-+ 
      |F|NRI|  Type   | 
      +---------------+ 
    
   This section specifies the semantics of F and NRI according to this 
   specification. 

   F: 1 bit 
      forbidden_zero_bit.  A value of 0 indicates that the NAL unit 
      type octet and payload should not contain bit errors or other 
      syntax violations.  A value of 1 indicates that the NAL unit type 
      octet and payload may contain bit errors or other syntax 
      violations. 

      MANEs SHOULD set the F bit to indicate detected bit errors in the 
      NAL unit.  The H.264 specification requires that the F bit is 
      equal to 0.  When the F bit is set, the decoder is advised that 
      bit errors or any other syntax violations may be present in the 
      payload or in the NAL unit type octet.  The simplest decoder 
 
 
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      reaction to a NAL unit in which the F bit is equal to 1 is to 
      discard such a NAL unit and to conceal the lost data in the 
      discarded NAL unit. 

   NRI: 2 bits 
      nal_ref_idc.  The semantics of value 00 and a non-zero value 
      remain unchanged from the H.264 specification.  In other words, a 
      value of 00 indicates that the content of the NAL unit is not 
      used to reconstruct reference pictures for inter picture 
      prediction. Such NAL units can be discarded without risking the 
      integrity of the reference pictures.  Values greater than 00 
      indicate that the decoding of the NAL unit is required to 
      maintain the integrity of the reference pictures. 

      In addition to the specification above, according to this RTP 
      payload specification, values of NRI indicate the relative 
      transport priority, as determined by the encoder.  MANEs can use 
      this information to protect more important NAL units better than 
      they do less important NAL units.  The highest transport priority 
      is 11, followed by 10, and then by 01; finally, 00 is the lowest. 

         Informative note: Any non-zero value of NRI is handled 
         identically in H.264 decoders.  Therefore, receivers need not 
         manipulate the value of NRI when passing NAL units to the 
         decoder. 

      An H.264 encoder MUST set the value of NRI according to the H.264 
      specification (subclause 7.4.1) when the value of nal_unit_type 
      is in the range of 1 to 12, inclusive.  In particular, the H.264 
      specification requires that the value of NRI SHALL be equal to 0 
      for all NAL units having nal_unit_type equal to 6, 9, 10, 11, or 
      12. 

      For NAL units having nal_unit_type equal to 7 or 8 (indicating a 
      sequence parameter set or a picture parameter set, respectively), 
      an H.264 encoder SHOULD set the value of NRI to 11 (in binary 
      format).  For coded slice NAL units of a primary coded picture 
      having nal_unit_type equal to 5 (indicating a coded slice 
      belonging to an IDR picture), an H.264 encoder SHOULD set the 
      value of NRI to 11 (in binary format). 

      For a mapping of the remaining nal_unit_types to NRI values, the 
      following example MAY be used and has been shown to be efficient 
      in a certain environment [13].  Other mappings MAY also be 
      desirable, depending on the application and the H.264/AVC Annex A 
      profile in use. 

 
 
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         Informative note: Data Partitioning is not available in 
         certain profiles; e.g., in the Main or Baseline profiles. 
         Consequently, the NAL unit types 2, 3, and 4 can occur only if 
         the video bitstream conforms to a profile in which data 
         partitioning is allowed and not in streams that conform to the 
         Main or Baseline profiles. 

   Table 2.  Example of NRI values for coded slices and coded slice data 
              partitions of primary coded reference pictures 

      NAL Unit Type     Content of NAL unit              NRI (binary) 
      ---------------------------------------------------------------- 
       1              non-IDR coded slice                         10 
       2              Coded slice data partition A                10 
       3              Coded slice data partition B                01 
       4              Coded slice data partition C                01 
    
         Informative note: As mentioned before, the NRI value of non-
         reference pictures is 00 as mandated by H.264/AVC. 

      An H.264 encoder SHOULD set the value of NRI for coded slice and 
      coded slice data partition NAL units of redundant coded reference 
      pictures equal to 01 (in binary format). 

      Definitions of the values for NRI for NAL unit types 24 to 29, 
      inclusive, are given in sections 5.7 and 5.8 of this memo. 

      No recommendation for the value of NRI is given for NAL units 
      having nal_unit_type in the range of 13 to 23, inclusive, because 
      these values are reserved for ITU-T and ISO/IEC.  No 
      recommendation for the value of NRI is given for NAL units having 
      nal_unit_type equal to 0 or in the range of 30 to 31, inclusive, 
      as the semantics of these values are not specified in this memo. 

5.4. Packetization Modes 

   This memo specifies three cases of packetization modes: 

   o  Single NAL unit mode 

   o  Non-interleaved mode 

   o  Interleaved mode 

   The single NAL unit mode is targeted for conversational systems that 
   comply with ITU-T Recommendation H.241 [15] (see section 12.1).  The 
   non-interleaved mode is targeted for conversational systems that may 
 
 
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   not comply with ITU-T Recommendation H.241.  In the non-interleaved 
   mode, NAL units are transmitted in NAL unit decoding order.  The 
   interleaved mode is targeted for systems that do not require very low 
   end-to-end latency.  The interleaved mode allows transmission of NAL 
   units out of NAL unit decoding order. 

   The packetization mode in use MAY be signaled by the value of the 
   OPTIONAL packetization-mode MIME parameter.  The used packetization 
   mode governs which NAL unit types are allowed in RTP payloads.  Table 
   3 summarizes the allowed packet payload types for each packetization 
   mode.  Packetization modes are explained in more detail in section 6. 

    Table 3.  Summary of allowed NAL unit types for each packetization 
            mode (yes = allowed, no = disallowed, ig = ignore) 

      Payload Packet    Single NAL    Non-Interleaved    Interleaved 
      Type    Type      Unit Mode           Mode             Mode 
      ------------------------------------------------------------- 
      0      undefined     ig               ig               ig 
      1-23   NAL unit     yes              yes               no 
      24     STAP-A        no              yes               no 
      25     STAP-B        no               no              yes 
      26     MTAP16        no               no              yes 
      27     MTAP24        no               no              yes 
      28     FU-A          no              yes              yes 
      29     FU-B          no               no              yes 
      30-31  undefined     ig               ig               ig 
 
   Some UAL unit or payload type values (indicated as undefined in Table 
   3) are reserved for future extensions.  NAL units of those types 
   SHOULD NOT be sent by a sender (direct as packet payloads, or as 
   aggregation units in aggregation packets, or as fragmented units in 
   FU packets) and MUST be ignored by a receiver.  For example, the 
   payload types 1-23, with the associated packet type "NAL unit", are 
   allowed in "Single NAL Unit Mode" and in "Non-Interleaved Mode", but 
   disallowed in "Interleaved Mode".  However, NAL units of NAL unit 
   types 1-23 can be used in "Interleaved Mode" as aggregation units in 
   STAP-B, MTAP16 and MTAP14 packets as well as fragmented units in FU-A 
   and FU-B packets.  Similarly, NAL units of NAL unit types 1-23 can 
   also be used in the "Non-Interleaved Mode" as aggregation units in 
   STAP-A packets or fragmented units in FU-A packets, in addition to 
   being directly used as packet payloads.   

5.5. Decoding Order Number (DON) 

   In the interleaved packetization mode, the transmission order of NAL 
   units is allowed to differ from the decoding order of the NAL units.  
 
 
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   Decoding order number (DON) is a field in the payload structure or a 
   derived variable that indicates the NAL unit decoding order.  
   Rationale and examples of use cases for transmission out of decoding 
   order and for the use of DON are given in section 13. 

   The coupling of transmission and decoding order is controlled by the 
   OPTIONAL sprop-interleaving-depth MIME parameter as follows.  When 
   the value of the OPTIONAL sprop-interleaving-depth MIME parameter is 
   equal to 0 (explicitly or per default), the transmission order of NAL 
   units MUST conform to the NAL unit decoding order.  When the value of 
   the OPTIONAL sprop-interleaving-depth MIME parameter is greater than 
   0, 

   o  the order of NAL units in an MTAP16 and an MTAP24 is NOT REQUIRED 
      to be the NAL unit decoding order, and 

   o  the order of NAL units generated by decapsulating STAP-Bs, MTAPs, 
      and FUs in two consecutive packets is NOT REQUIRED to be the NAL 
      unit decoding order. 

   The RTP payload structures for a single NAL unit packet, an STAP-A, 
   and an FU-A do not include DON.  STAP-B and FU-B structures include 
   DON, and the structure of MTAPs enables derivation of DON as 
   specified in section 5.7.2. 

      Informative note: When an FU-A occurs in interleaved mode, it 
      always follows an FU-B, which sets its DON. 

      Informative note: If a transmitter wants to encapsulate a single 
      NAL unit per packet and transmit packets out of their decoding 
      order, STAP-B packet type can be used. 

   In the single NAL unit packetization mode, the transmission order of 
   NAL units, determined by the RTP sequence number, MUST be the same as 
   their NAL unit decoding order.  In the non-interleaved packetization 
   mode, the transmission order of NAL units in single NAL unit packets, 
   STAP-As, and FU-As MUST be the same as their NAL unit decoding order.  
   The NAL units within an STAP MUST appear in the NAL unit decoding 
   order.  Thus, the decoding order is first provided through the 
   implicit order within a STAP, and second provided through the RTP 
   sequence number for the order between STAPs, FUs, and single NAL unit 
   packets. 

   Signaling of the value of DON for NAL units carried in STAP-B, MTAP, 
   and a series of fragmentation units starting with an FU-B is 
   specified in sections 5.7.1, 5.7.2, and 5.8, respectively.  The DON 
   value of the first NAL unit in transmission order MAY be set to any 
 
 
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   value.  Values of DON are in the range of 0 to 65535, inclusive.  
   After reaching the maximum value, the value of DON wraps around to 0. 

   The decoding order of two NAL units contained in any STAP-B, MTAP, or 
   a series of fragmentation units starting with an FU-B is determined 
   as follows.  Let DON(i) be the decoding order number of the NAL unit 
   having index i in the transmission order.  Function don_diff(m,n) is 
   specified as follows: 

         If DON(m) == DON(n), don_diff(m,n) = 0 

         If (DON(m) < DON(n) and DON(n) - DON(m) < 32768), 
         don_diff(m,n) = DON(n) - DON(m) 

         If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768), 
         don_diff(m,n) = 65536 - DON(m) + DON(n) 

         If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768), 
         don_diff(m,n) = - (DON(m) + 65536 - DON(n)) 

         If (DON(m) > DON(n) and DON(m) - DON(n) < 32768), 
         don_diff(m,n) = - (DON(m) - DON(n)) 

   A positive value of don_diff(m,n) indicates that the NAL unit having 
   transmission order index n follows, in decoding order, the NAL unit 
   having transmission order index m.  When don_diff(m,n) is equal to 0, 
   then the NAL unit decoding order of the two NAL units can be in 
   either order.  A negative value of don_diff(m,n) indicates that the 
   NAL unit having transmission order index n precedes, in decoding 
   order, the NAL unit having transmission order index m. 

   Values of DON related fields (DON, DONB, and DOND; see section 5.7) 
   MUST be such that the decoding order determined by the values of DON, 
   as specified above, conforms to the NAL unit decoding order.  If the 
   order of two NAL units in NAL unit decoding order is switched and the 
   new order does not conform to the NAL unit decoding order, the NAL 
   units MUST NOT have the same value of DON.  If the order of two 
   consecutive NAL units in the NAL unit stream is switched and the new 
   order still conforms to the NAL unit decoding order, the NAL units 
   MAY have the same value of DON.  For example, when arbitrary slice 
   order is allowed by the video coding profile in use, all the coded 
   slice NAL units of a coded picture are allowed to have the same value 
   of DON.  Consequently, NAL units having the same value of DON can be 
   decoded in any order, and two NAL units having a different value of 
   DON should be passed to the decoder in the order specified above.  
   When two consecutive NAL units in the NAL unit decoding order have a 
   different value of DON, the value of DON for the second NAL unit in 
 
 
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   decoding order SHOULD be the value of DON for the first, incremented 
   by one. 

   An example of the decapsulation process to recover the NAL unit 
   decoding order is given in section 7. 

      Informative note: Receivers should not expect that the absolute 
      difference of values of DON for two consecutive NAL units in the 
      NAL unit decoding order will be equal to one, even in error-free 
      transmission.  An increment by one is not required, as at the 
      time of associating values of DON to NAL units, it may not be 
      known whether all NAL units are delivered to the receiver.  For 
      example, a gateway may not forward coded slice NAL units of non-
      reference pictures or SEI NAL units when there is a shortage of 
      bit rate in the network to which the packets are forwarded.  In 
      another example, a live broadcast is interrupted by pre-encoded 
      content, such as commercials, from time to time.  The first intra 
      picture of a pre-encoded clip is transmitted in advance to ensure 
      that it is readily available in the receiver.  When transmitting 
      the first intra picture, the originator does not exactly know how 
      many NAL units will be encoded before the first intra picture of 
      the pre-encoded clip follows in decoding order.  Thus, the values 
      of DON for the NAL units of the first intra picture of the pre-
      encoded clip have to be estimated when they are transmitted, and 
      gaps in values of DON may occur. 

5.6. Single NAL Unit Packet 

   The single NAL unit packet defined here MUST contain only one NAL 
   unit, of the types defined in [1].  This means that neither an 
   aggregation packet nor a fragmentation unit can be used within a 
   single NAL unit packet.  A NAL unit stream composed by decapsulating 
   single NAL unit packets in RTP sequence number order MUST conform to 
   the NAL unit decoding order.  The structure of the single NAL unit 
   packet is shown in Figure 2. 

      Informative note: The first byte of a NAL unit co-serves as the 
      RTP payload header. 









 
 
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    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |F|NRI|  Type   |                                               | 
   +-+-+-+-+-+-+-+-+                                               | 
   |                                                               | 
   |               Bytes 2..n of a Single NAL unit                 | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
          Figure 2 RTP payload format for single NAL unit packet 

5.7. Aggregation Packets 

   Aggregation packets are the NAL unit aggregation scheme of this 
   payload specification.  The scheme is introduced to reflect the 
   dramatically different MTU sizes of two key target networks: wireline 
   IP networks (with an MTU size that is often limited by the Ethernet 
   MTU size; roughly 1500 bytes), and IP or non-IP (e.g., ITU-T H.324/M) 
   based wireless communication systems with preferred transmission unit 
   sizes of 254 bytes or less.  To prevent media transcoding between the 
   two worlds, and to avoid undesirable packetization overhead, a NAL 
   unit aggregation scheme is introduced. 

   Two types of aggregation packets are defined by this specification: 

   o  Single-time aggregation packet (STAP): aggregates NAL units with 
      identical NALU-time.  Two types of STAPs are defined, one without 
      DON (STAP-A) and another including DON (STAP-B). 

   o  Multi-time aggregation packet (MTAP): aggregates NAL units with 
      potentially differing NALU-time.  Two different MTAPs are defined, 
      differing in the length of the NAL unit timestamp offset. 

   Each NAL unit to be carried in an aggregation packet is encapsulated 
   in an aggregation unit.  Please see below for the four different 
   aggregation units and their characteristics. 

   The structure of the RTP payload format for aggregation packets is 
   presented in Figure 3. 





 
 
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    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |F|NRI|  Type   |                                               | 
   +-+-+-+-+-+-+-+-+                                               | 
   |                                                               | 
   |             one or more aggregation units                     | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
            Figure 3 RTP payload format for aggregation packets 

   MTAPs and STAPs share the following packetization rules:  The RTP 
   timestamp MUST be set to the earliest of the NALU-times of all the 
   NAL units to be aggregated.  The type field of the NAL unit type 
   octet MUST be set to the appropriate value, as indicated in Table 4.  
   The F bit MUST be cleared if all F bits of the aggregated NAL units 
   are zero; otherwise, it MUST be set.  The value of NRI MUST be the 
   maximum of all the NAL units carried in the aggregation packet. 

                 Table 4.  Type field for STAPs and MTAPs 

      Type   Packet    Timestamp offset   DON related fields 
                       field length       (DON, DONB, DOND) 
                       (in bits)          present 
      -------------------------------------------------------- 
      24     STAP-A       0                 no 
      25     STAP-B       0                 yes 
      26     MTAP16      16                 yes 
      27     MTAP24      24                 yes 
    
   The marker bit in the RTP header is set to the value that the marker 
   bit of the last NAL unit of the aggregated packet would have if it 
   were transported in its own RTP packet. 

   The payload of an aggregation packet consists of one or more 
   aggregation units.  See sections 5.7.1 and 5.7.2 for the four 
   different types of aggregation units.  An aggregation packet can 
   carry as many aggregation units as necessary; however, the total 
   amount of data in an aggregation packet obviously MUST fit into an IP 
   packet, and the size SHOULD be chosen so that the resulting IP packet 
   is smaller than the MTU size.  An aggregation packet MUST NOT contain 
   fragmentation units specified in section 5.8.  Aggregation packets 
   MUST NOT be nested; i.e., an aggregation packet MUST NOT contain 
   another aggregation packet. 
 
 
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5.7.1. Single-Time Aggregation Packet 

   Single-time aggregation packet (STAP) SHOULD be used whenever NAL 
   units are aggregated that all share the same NALU-time.  The payload 
   of an STAP-A does not include DON and consists of at least one 
   single-time aggregation unit, as presented in Figure 4.  The payload 
   of an STAP-B consists of a 16-bit unsigned decoding order number 
   (DON) (in network byte order) followed by at least one single-time 
   aggregation unit, as presented in Figure 5. 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
                   :                                               | 
   +-+-+-+-+-+-+-+-+                                               | 
   |                                                               | 
   |                single-time aggregation units                  | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               : 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
                    Figure 4 Payload format for STAP-A 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
                   :  decoding order number (DON)  |               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               | 
   |                                                               | 
   |                single-time aggregation units                  | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               : 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
                    Figure 5 Payload format for STAP-B 

   The DON field specifies the value of DON for the first NAL unit in an 
   STAP-B in transmission order.  For each successive NAL unit in 
   appearance order in an STAP-B, the value of DON is equal to (the 
   value of DON of the previous NAL unit in the STAP-B + 1) % 65536, in 
   which '%' stands for the modulo operation. 

   A single-time aggregation unit consists of 16-bit unsigned size 
   information (in network byte order) that indicates the size of the 
   following NAL unit in bytes (excluding these two octets, but 
 
 
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   including the NAL unit type octet of the NAL unit), followed by the 
   NAL unit itself, including its NAL unit type byte.  A single-time 
   aggregation unit is byte aligned within the RTP payload, but it may 
   not be aligned on a 32-bit word boundary.  Figure 6 presents the 
   structure of the single-time aggregation unit. 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
                   :        NAL unit size          |               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               | 
   |                                                               | 
   |                           NAL unit                            | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               : 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
            Figure 6 Structure for single-time aggregation unit 

   Figure 7 presents an example of an RTP packet that contains an STAP-
   A.  The STAP contains two single-time aggregation units, labeled as 1 
   and 2 in the figure. 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                          RTP Header                           | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |STAP-A NAL HDR |         NALU 1 Size           | NALU 1 HDR    | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                         NALU 1 Data                           | 
   :                                                               : 
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |               | NALU 2 Size                   | NALU 2 HDR    | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                         NALU 2 Data                           | 
   :                                                               : 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
 
    Figure 7 An example of an RTP packet including an STAP-A containing 
                     two single-time aggregation units 



 
 
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   Figure 8 presents an example of an RTP packet that contains an STAP-
   B.  The STAP contains two single-time aggregation units, labeled as 1 
   and 2 in the figure. 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                          RTP Header                           | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |STAP-B NAL HDR | DON                           | NALU 1 Size   | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   | NALU 1 Size   | NALU 1 HDR    | NALU 1 Data                   | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               + 
   :                                                               : 
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |               | NALU 2 Size                   | NALU 2 HDR    | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                       NALU 2 Data                             | 
   :                                                               : 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
    Figure 8 An example of an RTP packet including an STAP-B containing 
                     two single-time aggregation units 

5.7.2. Multi-Time Aggregation Packets (MTAPs) 

   The NAL unit payload of MTAPs consists of a 16-bit unsigned decoding 
   order number base (DONB) (in network byte order) and one or more 
   multi-time aggregation units, as presented in Figure 9.  DONB MUST 
   contain the value of DON for the first NAL unit in the NAL unit 
   decoding order among the NAL units of the MTAP. 

      Informative note: The first NAL unit in the NAL unit decoding 
      order is not necessarily the first NAL unit in the order in which 
      the NAL units are encapsulated in an MTAP. 










 
 
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    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
                   :  decoding order number base   |               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               | 
   |                                                               | 
   |                 multi-time aggregation units                  | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               : 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
                Figure 9 NAL unit payload format for MTAPs 

   Two different multi-time aggregation units are defined in this 
   specification.  Both of them consist of 16 bits unsigned size 
   information of the following NAL unit (in network byte order), an 8-
   bit unsigned decoding order number difference (DOND), and n bits (in 
   network byte order) of timestamp offset (TS offset) for this NAL 
   unit, whereby n can be 16 or 24.  The choice between the different 
   MTAP types (MTAP16 and MTAP24) is application dependent: the larger 
   the timestamp offset is, the higher the flexibility of the MTAP, but 
   the overhead is also higher. 

   The structure of the multi-time aggregation units for MTAP16 and 
   MTAP24 are presented in Figures 10 and 11, respectively.  The 
   starting or ending position of an aggregation unit within a packet is 
   NOT REQUIRED to be on a 32-bit word boundary.  The DON of the NAL 
   unit contained in a multi-time aggregation unit is equal to (DONB + 
   DOND) % 65536, in which % denotes the modulo operation.  This memo 
   does not specify how the NAL units within an MTAP are ordered, but, 
   in most cases, NAL unit decoding order SHOULD be used. 

   The timestamp offset field MUST be set to a value equal to the value 
   of the following formula: If the NALU-time is larger than or equal to 
   the RTP timestamp of the packet, then the timestamp offset equals 
   (the NALU-time of the NAL unit - the RTP timestamp of the packet).  
   If the NALU-time is smaller than the RTP timestamp of the packet, 
   then the timestamp offset is equal to the NALU-time + (2^32 - the RTP 
   timestamp of the packet). 







 
 
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    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   :        NAL unit size          |      DOND     |  TS offset    | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |  TS offset    |                                               | 
   +-+-+-+-+-+-+-+-+              NAL unit                         | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               : 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
             Figure 10  Multi-time aggregation unit for MTAP16 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   :        NAL unit size         |      DOND     |  TS offset    | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |         TS offset             |                               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               | 
   |                              NAL unit                         | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               : 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
             Figure 11  Multi-time aggregation unit for MTAP24 

   For the "earliest" multi-time aggregation unit in an MTAP the 
   timestamp offset MUST be zero.  Hence, the RTP timestamp of the MTAP 
   itself is identical to the earliest NALU-time. 

      Informative note: The "earliest" multi-time aggregation unit is 
      the one that would have the smallest extended RTP timestamp among 
      all the aggregation units of an MTAP if the NAL units contained 
      in the aggregation units were encapsulated in single NAL unit 
      packets.  An extended timestamp is a timestamp that has more than 
      32 bits and is capable of counting the wraparound of the 
      timestamp field, thus enabling one to determine the smallest 
      value if the timestamp wraps.  Such an "earliest" aggregation 
      unit may not be the first one in the order in which the 
      aggregation units are encapsulated in an MTAP.  The "earliest" 
      NAL unit need not be the same as the first NAL unit in the NAL 
      unit decoding order either. 



 
 
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   Figure 12 presents an example of an RTP packet that contains a multi-
   time aggregation packet of type MTAP16 that contains two multi-time 
   aggregation units, labeled as 1 and 2 in the figure. 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                          RTP Header                           | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |MTAP16 NAL HDR |  decoding order number base   | NALU 1 Size   | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |  NALU 1 Size  |  NALU 1 DOND  |       NALU 1 TS offset        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |  NALU 1 HDR   |  NALU 1 DATA                                  | 
   +-+-+-+-+-+-+-+-+                                               + 
   :                                                               : 
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |               | NALU 2 SIZE                   |  NALU 2 DOND  | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |       NALU 2 TS offset        |  NALU 2 HDR   |  NALU 2 DATA  | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+               | 
   :                                                               : 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
   Figure 12  An RTP packet including a multi-time aggregation packet of 
          type MTAP16 containing two multi-time aggregation units 

   Figure 13 presents an example of an RTP packet that contains a multi-
   time aggregation packet of type MTAP24 that contains two multi-time 
   aggregation units, labeled as 1 and 2 in the figure. 















 
 
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    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                          RTP Header                           | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |MTAP24 NAL HDR |  decoding order number base   | NALU 1 Size   | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |  NALU 1 Size  |  NALU 1 DOND  |       NALU 1 TS offs          | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |NALU 1 TS offs |  NALU 1 HDR   |  NALU 1 DATA                  | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               + 
   :                                                               : 
   +               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |               | NALU 2 SIZE                   |  NALU 2 DOND  | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |       NALU 2 TS offset                        |  NALU 2 HDR   | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |  NALU 2 DATA                                                  | 
   :                                                               : 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
   Figure 13  An RTP packet including a multi-time aggregation packet of 
          type MTAP24 containing two multi-time aggregation units 

5.7.3. Fragmentation Units (FUs) 

   This payload type allows fragmenting a NAL unit into several RTP 
   packets.  Doing so on the application layer instead of relying on 
   lower layer fragmentation (e.g., by IP) has the following advantages: 

   o  The payload format is capable of transporting NAL units bigger 
      than 64 kbytes over an IPv4 network that may be present in pre-
      recorded video, particularly in High Definition formats (there is 
      a limit of the number of slices per picture, which results in a 
      limit of NAL units per picture, which may result in big NAL 
      units). 

   o  The fragmentation mechanism allows fragmenting a single NAL unit 
      and applying generic forward error correction as described in 
      section 12.5. 

   Fragmentation is defined only for a single NAL unit and not for any 
   aggregation packets.  A fragment of a NAL unit consists of an integer 
   number of consecutive octets of that NAL unit.  Each octet of the NAL 
   unit MUST be part of exactly one fragment of that NAL unit.  
 
 
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   Fragments of the same NAL unit MUST be sent in consecutive order with 
   ascending RTP sequence numbers (with no other RTP packets within the 
   same RTP packet stream being sent between the first and last 
   fragment).  Similarly, a NAL unit MUST be reassembled in RTP sequence 
   number order. 

   When a NAL unit is fragmented and conveyed within fragmentation units 
   (FUs), it is referred to as a fragmented NAL unit.  STAPs and MTAPs 
   MUST NOT be fragmented.  FUs MUST NOT be nested; i.e., an FU MUST NOT 
   contain another FU. 

   The RTP timestamp of an RTP packet carrying an FU is set to the NALU-
   time of the fragmented NAL unit. 

   Figure 14 presents the RTP payload format for FU-As.  An FU-A 
   consists of a fragmentation unit indicator of one octet, a 
   fragmentation unit header of one octet, and a fragmentation unit 
   payload. 

    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   | FU indicator  |   FU header   |                               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               | 
   |                                                               | 
   |                         FU payload                            | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
                  Figure 14  RTP payload format for FU-A 

   Figure 15 presents the RTP payload format for FU-Bs.  An FU-B 
   consists of a fragmentation unit indicator of one octet, a 
   fragmentation unit header of one octet, a decoding order number (DON) 
   (in network byte order), and a fragmentation unit payload.  In other 
   words, the structure of FU-B is the same as the structure of FU-A, 
   except for the additional DON field. 








 
 
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    0                   1                   2                   3 
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   | FU indicator  |   FU header   |               DON             | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-| 
   |                                                               | 
   |                         FU payload                            | 
   |                                                               | 
   |                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                               :...OPTIONAL RTP padding        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
    
                  Figure 15  RTP payload format for FU-B 

   NAL unit type FU-B MUST be used in the interleaved packetization mode 
   for the first fragmentation unit of a fragmented NAL unit.  NAL unit 
   type FU-B MUST NOT be used in any other case.  In other words, in the 
   interleaved packetization mode, each NALU that is fragmented has an 
   FU-B as the first fragment, followed by one or more FU-A fragments. 

   The FU indicator octet has the following format: 

      +---------------+ 
      |0|1|2|3|4|5|6|7| 
      +-+-+-+-+-+-+-+-+ 
      |F|NRI|  Type   | 
      +---------------+ 
    
   Values equal to 28 and 29 in the Type field of the FU indicator octet 
   identify an FU-A and an FU-B, respectively.  The use of the F bit is 
   described in section 5.3.  The value of the NRI field MUST be set 
   according to the value of the NRI field in the fragmented NAL unit. 

   The FU header has the following format: 

      +---------------+ 
      |0|1|2|3|4|5|6|7| 
      +-+-+-+-+-+-+-+-+ 
      |S|E|R|  Type   | 
      +---------------+ 
    
   S: 1 bit 
      When set to one, the Start bit indicates the start of a 
      fragmented NAL unit.  When the following FU payload is not the 
      start of a fragmented NAL unit payload, the Start bit is set to 
      zero. 

 
 
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   E: 1 bit 
      When set to one, the End bit indicates the end of a fragmented 
      NAL unit, i.e., the last byte of the payload is also the last 
      byte of the fragmented NAL unit.  When the following FU payload 
      is not the last fragment of a fragmented NAL unit, the End bit is 
      set to zero. 

   R: 1 bit 
      The Reserved bit MUST be equal to 0 and MUST be ignored by the 
      receiver. 

   Type: 5 bits 
      The NAL unit payload type as defined in table 7-1 of [1]. 

   The value of DON in FU-Bs is selected as described in section 5.5. 

      Informative note: The DON field in FU-Bs allows gateways to 
      fragment NAL units to FU-Bs without organizing the incoming NAL 
      units to the NAL unit decoding order. 

   A fragmented NAL unit MUST NOT be transmitted in one FU; i.e., the 
   Start bit and End bit MUST NOT both be set to one in the same FU 
   header. 

   The FU payload consists of fragments of the payload of the fragmented 
   NAL unit so that if the fragmentation unit payloads of consecutive 
   FUs are sequentially concatenated, the payload of the fragmented NAL 
   unit can be reconstructed.  The NAL unit type octet of the fragmented 
   NAL unit is not included as such in the fragmentation unit payload, 
   but rather the information of the NAL unit type octet of the 
   fragmented NAL unit is conveyed in F and NRI fields of the FU 
   indicator octet of the fragmentation unit and in the type field of 
   the FU header.  An FU payload MAY have any number of octets and MAY 
   be empty. 

      Informative note: Empty FUs are allowed to reduce the latency of 
      a certain class of senders in nearly lossless environments.  
      These senders can be characterized in that they packetize NALU 
      fragments before the NALU is completely generated and, hence, 
      before the NALU size is known.  If zero-length NALU fragments 
      were not allowed, the sender would have to generate at least one 
      bit of data of the following fragment before the current fragment 
      could be sent.  Due to the characteristics of H.264, where 
      sometimes several macroblocks occupy zero bits, this is 
      undesirable and can add delay.  However, the (potential) use of 
      zero-length NALU fragments should be carefully weighed against 

 
 
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      the increased risk of the loss of at least a part of the NALU 
      because of the additional packets employed for its transmission. 

   If a fragmentation unit is lost, the receiver SHOULD discard all 
   following fragmentation units in transmission order corresponding to 
   the same fragmented NAL unit. 

   A receiver in an endpoint or in a MANE MAY aggregate the first n-1 
   fragments of a NAL unit to an (incomplete) NAL unit, even if fragment 
   n of that NAL unit is not received.  In this case, the 
   forbidden_zero_bit of the NAL unit MUST be set to one to indicate a 
   syntax violation. 

6. Packetization Rules 

   The packetization modes are introduced in section 5.2.  The 
   packetization rules common to more than one of the packetization 
   modes are specified in section 6.1.  The packetization rules for the 
   single NAL unit mode, the non-interleaved mode, and the interleaved 
   mode are specified in sections 6.2, 6.3, and 6.4, respectively. 

6.1. Common Packetization Rules 

   All senders MUST enforce the following packetization rules regardless 
   of the packetization mode in use: 

   o  Coded slice NAL units or coded slice data partition NAL units 
      belonging to the same coded picture (and thus sharing the same RTP 
      timestamp value) MAY be sent in any order; however, for delay-
      critical systems, they SHOULD be sent in their original decoding 
      order to minimize the delay.  Note that the decoding order is the 
      order of the NAL units in the bitstream. 

   o  Parameter sets are handled in accordance with the rules and 
      recommendations given in section 8.4. 

   o  MANEs MUST NOT duplicate any NAL unit except for sequence or 
      picture parameter set NAL units, as neither this memo nor the 
      H.264 specification provides means to identify duplicated NAL 
      units.  Sequence and picture parameter set NAL units MAY be 
      duplicated to make their correct reception more probable, but any 
      such duplication MUST NOT affect the contents of any active 
      sequence or picture parameter set.  Duplication SHOULD be 
      performed on the application layer and not by duplicating RTP 
      packets (with identical sequence numbers). 


 
 
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   Senders using the non-interleaved mode and the interleaved mode MUST 
   enforce the following packetization rule: 

   o  MANEs MAY convert single NAL unit packets into one aggregation 
      packet, convert an aggregation packet into several single NAL unit 
      packets, or mix both concepts, in an RTP translator.  The RTP 
      translator SHOULD take into account at least the following 
      parameters: path MTU size, unequal protection mechanisms (e.g., 
      through packet-based FEC according to RFC 2733 [18], especially 
      for sequence and picture parameter set NAL units and coded slice 
      data partition A NAL units), bearable latency of the system, and 
      buffering capabilities of the receiver. 

         Informative note: An RTP translator is required to handle RTCP 
         as per RFC 3550. 

6.2. Single NAL Unit Mode 

   This mode is in use when the value of the OPTIONAL packetization-mode 
   MIME parameter is equal to 0 or the packetization-mode is not 
   present.  All receivers MUST support this mode.  It is primarily 
   intended for low-delay applications that are compatible with systems 
   using ITU-T Recommendation H.241 [15] (see section 12.1).  Only 
   single NAL unit packets MAY be used in this mode.  STAPs, MTAPs, and 
   FUs MUST NOT be used.  The transmission order of single NAL unit 
   packets MUST comply with the NAL unit decoding order. 

6.3. Non-Interleaved Mode 

   This mode is in use when the value of the OPTIONAL packetization-mode 
   MIME parameter is equal to 1.  This mode SHOULD be supported.  It is 
   primarily intended for low-delay applications.  Only single NAL unit 
   packets, STAP-As, and FU-As MAY be used in this mode.  STAP-Bs, 
   MTAPs, and FU-Bs MUST NOT be used.  The transmission order of NAL 
   units MUST comply with the NAL unit decoding order. 

6.4. Interleaved Mode 

   This mode is in use when the value of the OPTIONAL packetization-mode 
   MIME parameter is equal to 2.  Some receivers MAY support this mode.  
   STAP-Bs, MTAPs, FU-As, and FU-Bs MAY be used.  STAP-As and single NAL 
   unit packets MUST NOT be used.  The transmission order of packets and 
   NAL units is constrained as specified in section 5.5. 

 


 
 
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7. De-Packetization Process  

   The de-packetization process is implementation dependent.  Therefore, 
   the following description should be seen as an example of a suitable 
   implementation.  Other schemes may be used as well as long as the 
   output for the same input is the same as the process described below.  
   The output is the same meaning that the number of NAL units and their 
   order are both the identical.  Optimizations relative to the 
   described algorithms are likely possible.  Section 7.1 presents the 
   de-packetization process for the single NAL unit and non-interleaved 
   packetization modes, whereas section 7.2 describes the process for 
   the interleaved mode.  Section 7.3 includes additional decapsulation 
   guidelines for intelligent receivers. 

   All normal RTP mechanisms related to buffer management apply.  In 
   particular, duplicated or outdated RTP packets (as indicated by the 
   RTP sequences number and the RTP timestamp) are removed.  To 
   determine the exact time for decoding, factors such as a possible 
   intentional delay to allow for proper inter-stream synchronization 
   must be factored in. 

7.1. Single NAL Unit and Non-Interleaved Mode 

   The receiver includes a receiver buffer to compensate for 
   transmission delay jitter.  The receiver stores incoming packets in 
   reception order into the receiver buffer.  Packets are decapsulated 
   in RTP sequence number order.  If a decapsulated packet is a single 
   NAL unit packet, the NAL unit contained in the packet is passed 
   directly to the decoder.  If a decapsulated packet is an STAP-A, the 
   NAL units contained in the packet are passed to the decoder in the 
   order in which they are encapsulated in the packet.  For all the FU-A 
   packets containing fragments of a single NAL unit, the decapsulated 
   fragments are concatenated in their sending order to recover the NAL 
   unit, which is then passed to the decoder. 

      Informative note: If the decoder supports Arbitrary Slice Order, 
      coded slices of a picture can be passed to the decoder in any 
      order regardless of their reception and transmission order. 

7.2. Interleaved Mode 

   The general concept behind these de-packetization rules is to reorder 
   NAL units from transmission order to the NAL unit decoding order. 

   The receiver includes a receiver buffer, which is used to compensate 
   for transmission delay jitter and to reorder NAL units from 
   transmission order to the NAL unit decoding order.  In this section, 
 
 
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   the receiver operation is described under the assumption that there 
   is no transmission delay jitter.  To make a difference from a 
   practical receiver buffer that is also used for compensation of 
   transmission delay jitter, the receiver buffer is here after called 
   the deinterleaving buffer in this section.  Receivers SHOULD also 
   prepare for transmission delay jitter; i.e., either reserve separate 
   buffers for transmission delay jitter buffering and deinterleaving 
   buffering or use a receiver buffer for both transmission delay jitter 
   and deinterleaving.  Moreover, receivers SHOULD take transmission 
   delay jitter into account in the buffering operation; e.g., by 
   additional initial buffering before starting of decoding and 
   playback. 

   This section is organized as follows: subsection 7.2.1 presents how o 
   calculate the size of the deinterleaving buffer.  Subsection 7.2.2 
   specifies the receiver process how to organize received NAL units to 
   the NAL unit decoding order. 

7.2.1. Size of the Deinterleaving Buffer 

   When SDP Offer/Answer model or any other capability exchange 
   procedure is used in session setup, the properties of the received 
   stream SHOULD be such that the receiver capabilities are not 
   exceeded.  In the SDP Offer/Answer model, the receiver can indicate 
   its capabilities to allocate a deinterleaving buffer with the deint-
   buf-cap MIME parameter.  The sender indicates the requirement for the 
   deinterleaving buffer size with the sprop-deint-buf-req MIME 
   parameter.  It is therefore RECOMMENDED to set the deinterleaving 
   buffer size, in terms of number of bytes, equal to or greater than 
   the value of sprop-deint-buf-req MIME parameter.  See section 8.1 for 
   further information on deint-buf-cap and sprop-deint-buf-req MIME 
   parameters and section 8.2.2 for further information on their use in 
   SDP Offer/Answer model. 

   When a declarative session description is used in session setup, the 
   sprop-deint-buf-req MIME parameter signals the requirement for the 
   deinterleaving buffer size.  It is therefore RECOMMENDED to set the 
   deinterleaving buffer size, in terms of number of bytes, equal to or 
   greater than the value of sprop-deint-buf-req MIME parameter. 

7.2.2. Deinterleaving Process 

   There are two buffering states in the receiver: initial buffering and 
   buffering while playing.  Initial buffering occurs when the RTP 
   session is initialized.  After initial buffering, decoding and 
   playback are started, and the buffering-while-playing mode is used. 

 
 
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   Regardless of the buffering state, the receiver stores incoming NAL 
   units, in reception order, in the deinterleaving buffer as follows.  
   NAL units of aggregation packets are stored in the deinterleaving 
   buffer individually.  The value of DON is calculated and stored for 
   each NAL unit. 

   The receiver operation is described below with the help of the 
   following functions and constants: 

   o  Function AbsDON is specified in section 8.1. 

   o  Function don_diff is specified in section 5.5. 

   o  Constant N is the value of the OPTIONAL sprop-interleaving-depth 
      MIME type parameter (see section 8.1) incremented by 1. 

   Initial buffering lasts until one of the following conditions is 
   fulfilled: 

   o  There are N or more VCL NAL units in the deinterleaving buffer. 

   o  If sprop-max-don-diff is present, don_diff(m,n) is greater than 
      the value of sprop-max-don-diff, in which n corresponds to the NAL 
      unit having the greatest value of AbsDON among the received NAL 
      units and m corresponds to the NAL unit having the smallest value 
      of AbsDON among the received NAL units. 

   o  Initial buffering has lasted for the duration equal to or greater 
      than the value of the OPTIONAL sprop-init-buf-time MIME parameter. 

   The NAL units to be removed from the deinterleaving buffer are 
   determined as follows: 

   o  If the deinterleaving buffer contains at least N VCL NAL units, 
      NAL units are removed from the deinterleaving buffer and passed to 
      the decoder in the order specified below until the buffer contains 
      N-1 VCL NAL units. 

   o  If sprop-max-don-diff is present, all NAL units m for which 
      don_diff(m,n) is greater than sprop-max-don-diff are removed from 
      the deinterleaving buffer and passed to the decoder in the order 
      specified below.  Herein, n corresponds to the NAL unit having the 
      greatest value of AbsDON among the NAL units in the deinterleaving 
      buffer. 

   The order in which NAL units are passed to the decoder is specified 
   as follows: 
 
 
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   o  Let PDON be a variable that is initialized to 0 at the beginning 
      of the RTP session. 

   o  For each NAL unit associated with a value of DON, a DON distance 
      is calculated as follows.  If the value of DON of the NAL unit is 
      larger than the value of PDON, the DON distance is equal to DON - 
      PDON.  Otherwise, the DON distance is equal to 65535 - PDON + DON 
      + 1. 

   o  NAL units are delivered to the decoder in ascending order of DON 
      distance.  If several NAL units share the same value of DON 
      distance, they can be passed to the decoder in any order. 

   o  When a desired number of NAL units have been passed to the 
      decoder, the value of PDON is set to the value of DON for the last 
      NAL unit passed to the decoder. 

7.3. Additional De-Packetization Guidelines 

   The following additional de-packetization rules may be used to 
   implement an operational H.264 de-packetizer: 

   o  Intelligent RTP receivers (e.g., in gateways) may identify lost 
      coded slice data partitions A (DPAs).  If a lost DPA is found, a 
      gateway may decide not to send the corresponding coded slice data 
      partitions B and C, as their information is meaningless for H.264 
      decoders.  In this way a MANE can reduce network load by 
      discarding useless packets without parsing a complex bitstream. 

   o  Intelligent RTP receivers (e.g., in gateways) may identify lost 
      FUs.  If a lost FU is found, a gateway may decide not to send the 
      following FUs of the same fragmented NAL unit, as their 
      information is meaningless for H.264 decoders.  In this way a MANE 
      can reduce network load by discarding useless packets without 
      parsing a complex bitstream. 

   o  Intelligent receivers having to discard packets or NALUs should 
      first discard all packets/NALUs in which the value of the NRI 
      field of the NAL unit type octet is equal to 0.  This will 
      minimize the impact on user experience and keep the reference 
      pictures intact.  If more packets have to be discarded, then 
      packets with a numerically lower NRI value should be discarded 
      before packets with a numerically higher NRI value.  However, 
      discarding any packets with an NRI bigger than 0 very likely leads 
      to decoder drift and SHOULD be avoided. 


 
 
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8. Payload Format Parameters 

   This section specifies the parameters that MAY be used to select 
   optional features of the payload format and certain features of the 
   bitstream.  The parameters are specified here as part of the MIME 
   subtype registration for the ITU-T H.264 | ISO/IEC 14496-10 codec.  A 
   mapping of the parameters into the Session Description Protocol (SDP) 
   [5] is also provided for applications that use SDP.  Equivalent 
   parameters could be defined elsewhere for use with control protocols 
   that do not use MIME or SDP. 

   Some parameters provide a receiver with the properties of the stream 
   that will be sent.  The names of all these parameters start with 
   "sprop" for stream properties.  Some of these "sprop" parameters are 
   limited by other payload or codec configuration parameters.  For 
   example, the sprop-parameter-sets parameter is constrained by the 
   profile-level-id parameter.  The media sender selects all "sprop" 
   parameters rather than the receiver.  This uncommon characteristic of 
   the "sprop" parameters may not be compatible with some signaling 
   protocol concepts, in which case the use of these parameters SHOULD 
   be avoided. 

8.1. MIME Registration 

   The MIME subtype for the ITU-T H.264 | ISO/IEC 14496-10 codec is 
   allocated from the IETF tree. 

   The receiver MUST ignore any unspecified parameter. 

   Media Type name:     video 

   Media subtype name:  H264 

   Required parameters: none 

   OPTIONAL parameters: 

      profile-level-id: 
         A base16 [6] (hexadecimal) representation of the following 
         three bytes in the sequence parameter set NAL unit specified 
         in [1]: 1) profile_idc, 2) a byte herein referred to as 
         profile-iop, composed of the values of constraint_set0_flag, 
         constraint_set1_flag,constraint_set2_flag, and 
         reserved_zero_5bits in bit-significance order, starting from 
         the most significant bit, and 3) level_idc.  Note that 
         reserved_zero_5bits is required to be equal to 0 in [1], but 

 
 
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         other values for it may be specified in the future by ITU-T or 
         ISO/IEC. 

         If the profile-level-id parameter is used to indicate 
         properties of a NAL unit stream, it indicates the profile and 
         level that a decoder has to support in order to comply with 
         [1] when it decodes the stream.  The profile-iop byte 
         indicates whether the NAL unit stream also obeys all 
         constraints of the indicated profiles as follows.  If bit 7 
         (the most significant bit), bit 6, or bit 5 of profile-iop is 
         equal to 1, all constraints of the Baseline profile, the Main 
         profile, or the Extended profile, respectively, are obeyed in 
         the NAL unit stream.  If the profile-level-id parameter is 
         used for capability exchange or session setup procedure, it 
         indicates the profile that the codec supports and the highest 
         level supported for the signaled profile.  The profile-iop 
         byte indicates whether the codec has additional limitations 
         whereby only the common subset of the algorithmic features and 
         limitations of the profiles signaled with the profile-iop byte 
         and of the profile indicated by profile_idc is supported by 
         the codec.  For example, if a codec supports only the common 
         subset of the coding tools of the Baseline profile and the 
         Main profile at level 2.1 and below, the profile-level-id 
         becomes 42E015, in which 42 stands for the Baseline profile, 
         E0 indicates that only the common subset for all profiles is 
         supported, and 15 indicates level 2.1. 

            Informative note: Capability exchange and session setup 
            procedures should provide means to list the capabilities 
            for each supported codec profile separately.  For example, 
            the one-of-N codec selection procedure of the SDP 
            Offer/Answer model can be used (section 10.2 of [7]). 

         If no profile-level-id is present, the Baseline Profile 
         without additional constraints at Level 1 MUST be implied. 

      max-mbps, max-fs, max-cpb, max-dpb, and max-br: 
         These parameters MAY be used to signal the capabilities of a 
         receiver implementation. These parameters MUST NOT be used for 
         any other purpose.  The profile-level-id parameter MUST be 
         present in the same receiver capability description that 
         contains any of these parameters.  The level conveyed in the 
         value of the profile-level-id parameter MUST be such that the 
         receiver is fully capable of supporting.  max-mbps, max-fs, 
         max-cpb, max-dpb, and max-br MAY be used to indicate 
         capabilities of the receiver that extend the required 
         capabilities of the signaled level, as specified below. 
 
 
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         When more than one parameter from the set (max-mbps, max-fs, 
         max-cpb, max-dpb, max-br) is present, the receiver MUST 
         support all signaled capabilities simultaneously.  For 
         example, if both max-mbps and max-br are present, the signaled 
         level with the extension of both the frame rate and bit rate 
         is supported.  That is, the receiver is able to decode NAL 
         unit streams in which the macroblock processing rate is up to 
         max-mbps (inclusive), the bit rate is up to max-br 
         (inclusive), the coded picture buffer size is derived as 
         specified in the semantics of the max-br parameter below, and 
         other properties comply with the level specified in the value 
         of the profile-level-id parameter. 

         If a receiver can support all the properties of level A, the 
         level specified in the value of the profile-level-id MUST be 
         level A (i.e. MUST NOT be lower than level A).  In other 
         words, a sender or receiver MUST NOT signal values of max-
         mbps, max-fs, max-cpb, max-dpb, and max-br that meet the 
         requirements of a higher level compared to the level specified 
         in the value of the profile-level-id parameter.  

            Informative note: When the OPTIONAL MIME type parameters 
            are used to signal the properties of a NAL unit stream, 
            max-mbps, max-fs, max-cpb, max-dpb, and max-br are not 
            present, and the value of profile-level-id must always be 
            such that the NAL unit stream complies fully with the 
            specified profile and level. 

      max-mbps: The value of max-mbps is an integer indicating the 
         maximum macroblock processing rate in units of macroblocks per 
         second.  The max-mbps parameter signals that the receiver is 
         capable of decoding video at a higher rate than is required by 
         the signaled level conveyed in the value of the profile-level-
         id parameter.  When max-mbps is signaled, the receiver MUST be 
         able to decode NAL unit streams that conform to the signaled 
         level, with the exception that the MaxMBPS value in Table A-1 
         of [1] for the signaled level is replaced with the value of 
         max-mbps.  The value of max-mbps MUST be greater than or equal 
         to the value of MaxMBPS for the level given in Table A-1 of 
         [1].  Senders MAY use this knowledge to send pictures of a 
         given size at a higher picture rate than is indicated in the 
         signaled level. 

      max-fs: The value of max-fs is an integer indicating the maximum 
         frame size in units of macroblocks.  The max-fs parameter 
         signals that the receiver is capable of decoding larger 
         picture sizes than are required by the signaled level conveyed 
 
 
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         in the value of the profile-level-id parameter.  When max-fs 
         is signaled, the receiver MUST be able to decode NAL unit 
         streams that conform to the signaled level, with the exception 
         that the MaxFS value in Table A-1 of [1] for the signaled 
         level is replaced with the value of max-fs.  The value of max-
         fs MUST be greater than or equal to the value of MaxFS for the 
         level given in Table A-1 of [1].  Senders MAY use this 
         knowledge to send larger pictures at a proportionally lower 
         frame rate than is indicated in the signaled level. 

      max-cpb: The value of max-cpb is an integer indicating the 
         maximum coded picture buffer size in units of 1000 bits for 
         the VCL HRD parameters (see A.3.1 item i of [1]) and in units 
         of 1200 bits for the NAL HRD parameters (see A.3.1 item j of 
         [1]).  The max-cpb parameter signals that the receiver has 
         more memory than the minimum amount of coded picture buffer 
         memory required by the signaled level conveyed in the value of 
         the profile-level-id parameter.  When max-cpb is signaled, the 
         receiver MUST be able to decode NAL unit streams that conform 
         to the signaled level, with the exception that the MaxCPB 
         value in Table A-1 of [1] for the signaled level is replaced 
         with the value of max-cpb.  The value of max-cpb MUST be 
         greater than or equal to the value of MaxCPB for the level 
         given in Table A-1 of [1].  Senders MAY use this knowledge to 
         construct coded video streams with greater variation of bit 
         rate than can be achieved with the MaxCPB value in Table A-1 
         of [1]. 

            Informative note: The coded picture buffer is used in the 
            hypothetical reference decoder (Annex C) of H.264.  The use 
            of the hypothetical reference decoder is recommended in 
            H.264 encoders to verify that the produced bitstream 
            conforms to the standard and to control the output bitrate.  
            Thus, the coded picture buffer is conceptually independent 
            of any other potential buffers in the receiver, including 
            de-interleaving and de-jitter buffers.  The coded picture 
            buffer need not be implemented in decoders as specified in 
            Annex C of H.264, but rather standard-compliant decoders 
            can have any buffering arrangements provided that they can 
            decode standard-compliant bitstreams.  Thus, in practice, 
            the input buffer for video decoder can be integrated with 
            de-interleaving and de-jitter buffers of the receiver. 

      max-dpb: The value of max-dpb is an integer indicating the 
         maximum decoded picture buffer size in units of 1024 bytes.  
         The max-dpb parameter signals that the receiver has more 
         memory than the minimum amount of decoded picture buffer 
 
 
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         memory required by the signaled level conveyed in the value of 
         the profile-level-id parameter.  When max-dpb is signaled, the 
         receiver MUST be able to decode NAL unit streams that conform 
         to the signaled level, with the exception that the MaxDPB 
         value in Table A-1 of [1] for the signaled level is replaced 
         with the value of max-dpb.  Consequently, a receiver that 
         signals max-dpb MUST be capable of storing the following 
         number of decoded frames, complementary field pairs, and non-
         paired fields in its decoded picture buffer: 

            Min(1024 * max-dpb / ( PicWidthInMbs * FrameHeightInMbs * 
            256 * ChromaFormatFactor ), 16) 

         PicWidthInMbs, FrameHeightInMbs, and ChromaFormatFactor are 
         defined in [1]. 

         The value of max-dpb MUST be greater than or equal to the 
         value of MaxDPB for the level given in Table A-1 of [1].  
         Senders MAY use this knowledge to construct coded video 
         streams with improved compression. 

            Informative note: This parameter was added primarily to 
            complement a similar codepoint in the ITU-T Recommendation 
            H.245, so as to facilitate signaling gateway designs.  The 
            decoded picture buffer stores reconstructed samples.  There 
            is no relationship between the size of the decoded picture 
            buffer and the buffers used in RTP, especially de-
            interleaving and de-jitter buffers. 

      max-br: The value of max-br is an integer indicating the maximum 
         video bit rate in units of 1000 bits per second for the VCL 
         HRD parameters (see A.3.1 item i of [1]) and in units of 1200 
         bits per second for the NAL HRD parameters (see A.3.1 item j 
         of [1]). 

         The max-br parameter signals that the video decoder of the 
         receiver is capable of decoding video at a higher bit rate 
         than is required by the signaled level conveyed in the value 
         of the profile-level-id parameter. 

         When max-br is signaled, the video codec of the receiver MUST 
         be able to decode NAL unit streams that conform to the 
         signaled level, conveyed in the profile-level-id parameter, 
         with the following exceptions in the limits specified by the 
         level: 


 
 
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         o The value of max-br replaces the MaxBR value of the signaled 
            level (in Table A-1 of [1]). 

         o When the max-cpb parameter is not present, the result of the 
            following formula replaces the value of MaxCPB in Table A-1 
            of [1]: (MaxCPB of the signaled level) * max-br / (MaxBR of 
            the signaled level). 

         For example, if a receiver signals capability for Level 1.2 
         with max-br equal to 1550, this indicates a maximum video 
         bitrate of 1550 kbits/sec for VCL HRD parameters, a maximum 
         video bitrate of 1860 kbits/sec for NAL HRD parameters, and a 
         CPB size of 4036458 bits (1550000 / 384000 * 1000 * 1000). 

         The value of max-br MUST be greater than or equal to the value 
         MaxBR for the signaled level given in Table A-1 of [1]. 

         Senders MAY use this knowledge to send higher bitrate video as 
         allowed in the level definition of Annex A of H.264, to 
         achieve improved video quality. 

            Informative note: This parameter was added primarily to 
            complement a similar codepoint in the ITU-T Recommendation 
            H.245, so as to facilitate signaling gateway designs.  No 
            assumption can be made from the value of this parameter 
            that the network is capable of handling such bit rates at 
            any given time.  In particular, no conclusion can be drawn 
            that the signaled bit rate is possible under congestion 
            control constraints. 

      redundant-pic-cap: 
         This parameter signals the capabilities of a receiver 
         implementation.  When equal to 0, the parameter indicates that 
         the receiver makes no attempt to use redundant coded pictures 
         to correct incorrectly decoded primary coded pictures.  When 
         equal to 0, the receiver is not capable of using redundant 
         slices; therefore, a sender SHOULD avoid sending redundant 
         slices to save bandwidth.  When equal to 1, the receiver is 
         capable of decoding any such redundant slice that covers a 
         corrupted area in a primary decoded picture (at least partly), 
         and therefore a sender MAY send redundant slices.  When the 
         parameter is not present, then a value of 0 MUST be used for 
         redundant-pic-cap.  When present, the value of redundant-pic-
         cap MUST be either 0 or 1. 

         When the profile-level-id parameter is present in the same 
         capability signaling as the redundant-pic-cap parameter, and 
 
 
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         the profile indicated in profile-level-id is such that it 
         disallows the use of redundant coded pictures (e.g., Main 
         Profile), the value of redundant-pic-cap MUST be equal to 0.  
         When a receiver indicates redundant-pic-cap equal to 0, the 
         received stream SHOULD NOT contain redundant coded pictures. 

            Informative note: Even if redundant-pic-cap is equal to 0, 
            the decoder is able to ignore redundant codec pictures 
            provided that the decoder supports such a profile 
            (Baseline, Extended) in which redundant coded pictures are 
            allowed. 

            Informative note: Even if redundant-pic-cap is equal to 1, 
            the receiver may also choose other error concealment 
            strategies to replace or complement decoding of redundant 
            slices. 

      sprop-parameter-sets: 
         This parameter MAY be used to convey any sequence and picture 
         parameter set NAL units (herein referred to as the initial 
         parameter set NAL units) that MUST precede any other NAL units 
         in decoding order.  The parameter MUST NOT be used to indicate 
         codec capability in any capability exchange procedure.  The 
         value of the parameter is the base64 [6] representation of the 
         initial parameter set NAL units as specified in sections 
         7.3.2.1 and 7.3.2.2 of [1].  The parameter sets are conveyed 
         in decoding order, and no framing of the parameter set NAL 
         units takes place.  A comma is used to separate any pair of 
         parameter sets in the list.  Note that the number of bytes in 
         a parameter set NAL unit is typically less than 10, but a 
         picture parameter set NAL unit can contain several hundreds of 
         bytes. 

            Informative note: When several payload types are offered in 
            the SDP Offer/Answer model, each with its own sprop-
            parameter-sets parameter, then the receiver cannot assume 
            that those parameter sets do not use conflicting storage 
            locations (i.e., identical values of parameter set 
            identifiers).  Therefore, a receiver should double-buffer 
            all sprop-parameter-sets and make them available to the 
            decoder instance that decodes a certain payload type. 

      packetization-mode: 
         This parameter signals the properties of an RTP payload type 
         or the capabilities of a receiver implementation.  Only a 
         single configuration point can be indicated; thus, when 
         capabilities to support more than one packetization-mode are 
 
 
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         declared, multiple configuration points (RTP payload types) 
         must be used. 

         When the value of packetization-mode is equal to 0 or 
         packetization-mode is not present, the single NAL mode, as 
         defined in section 6.2 of RFC 3984, MUST be used.  This mode 
         is in use in standards using ITU-T Recommendation H.241 [15] 
         (see section 12.1).  When the value of packetization-mode is 
         equal to 1, the non-interleaved mode, as defined in section 
         6.3 of RFC 3984, MUST be used.  When the value of 
         packetization-mode is equal to 2, the interleaved mode, as 
         defined in section 6.4 of RFC 3984, MUST be used.  The value 
         of packetization-mode MUST be an integer in the range of 0 to 
         2, inclusive. 

      sprop-interleaving-depth: 
         This parameter MUST NOT be present when packetization-mode is 
         not present or the value of packetization-mode is equal to 0 
         or 1.  This parameter MUST be present when the value of 
         packetization-mode is equal to 2. 

         This parameter signals the properties of an RTP packet stream.  
         It specifies the maximum number of VCL NAL units that precede 
         any VCL NAL unit in the RTP packet stream in transmission 
         order and follow the VCL NAL unit in decoding order.  
         Consequently, it is guaranteed that receivers can reconstruct 
         NAL unit decoding order when the buffer size for NAL unit 
         decoding order recovery is at least the value of sprop-
         interleaving-depth + 1 in terms of VCL NAL units. 

         The value of sprop-interleaving-depth MUST be an integer in 
         the range of 0 to 32767, inclusive. 

      sprop-deint-buf-req: 
         This parameter MUST NOT be present when packetization-mode is 
         not present or the value of packetization-mode is equal to 0 
         or 1.  It MUST be present when the value of packetization-mode 
         is equal to 2. 

         sprop-deint-buf-req signals the required size of the 
         deinterleaving buffer for the RTP packet stream.  The value of 
         the parameter MUST be greater than or equal to the maximum 
         buffer occupancy (in units of bytes) required in such a 
         deinterleaving buffer that is specified in section 7.2 of RFC 
         3984.  It is guaranteed that receivers can perform the 
         deinterleaving of interleaved NAL units into NAL unit decoding 

 
 
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         order, when the deinterleaving buffer size is at least the 
         value of sprop-deint-buf-req in terms of bytes. 

         The value of sprop-deint-buf-req MUST be an integer in the 
         range of 0 to 4294967295, inclusive. 

            Informative note: sprop-deint-buf-req indicates the 
            required size of the deinterleaving buffer only.  When 
            network jitter can occur, an appropriately sized jitter 
            buffer has to be provisioned for as well. 

      deint-buf-cap: 
         This parameter signals the capabilities of a receiver 
         implementation and indicates the amount of deinterleaving 
         buffer space in units of bytes that the receiver has available 
         for reconstructing the NAL unit decoding order.  A receiver is 
         able to handle any stream for which the value of the sprop-
         deint-buf-req parameter is smaller than or equal to this 
         parameter. 

         If the parameter is not present, then a value of 0 MUST be 
         used for deint-buf-cap.  The value of deint-buf-cap MUST be an 
         integer in the range of 0 to 4294967295, inclusive. 

            Informative note: deint-buf-cap indicates the maximum 
            possible size of the deinterleaving buffer of the receiver 
            only.  When network jitter can occur, an appropriately 
            sized jitter buffer has to be provisioned for as well. 

      sprop-init-buf-time: 
         This parameter MAY be used to signal the properties of an RTP 
         packet stream.  The parameter MUST NOT be present, if the 
         value of packetization-mode is equal to 0 or 1. 

         The parameter signals the initial buffering time that a 
         receiver MUST wait before starting decoding to recover the NAL 
         unit decoding order from the transmission order.  The 
         parameter is the maximum value of (decoding time of the NAL 
         unit - transmission time of a NAL unit), assuming reliable and 
         instantaneous transmission, the same timeline for transmission 
         and decoding, and that decoding starts when the first packet 
         arrives. 

         An example of specifying the value of sprop-init-buf-time 
         follows.  A NAL unit stream is sent in the following 
         interleaved order, in which the value corresponds to the 

 
 
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         decoding time and the transmission order is from left to 
         right: 

            0  2  1  3  5  4  6  8  7 ... 

         Assuming a steady transmission rate of NAL units, the 
         transmission times are: 

            0  1  2  3  4  5  6  7  8 ... 

         Subtracting the decoding time from the transmission time 
         column-wise results in the following series: 

            0 -1  1  0 -1  1  0 -1  1 ... 

         Thus, in terms of intervals of NAL unit transmission times, 
         the value of sprop-init-buf-time in this example is 1.  The 
         parameter is coded as a non-negative base10 integer 
         representation in clock ticks of a 90-kHz clock.  If the 
         parameter is not present, then no initial buffering time value 
         is defined.  Otherwise the value of sprop-init-buf-time MUST 
         be an integer in the range of 0 to 4294967295, inclusive. 

         In addition to the signaled sprop-init-buf-time, receivers 
         SHOULD take into account the transmission delay jitter 
         buffering, including buffering for the delay jitter caused by 
         mixers, translators, gateways, proxies, traffic-shapers, and 
         other network elements. 

      sprop-max-don-diff: 
         This parameter MAY be used to signal the properties of an RTP 
         packet stream.  It MUST NOT be used to signal transmitter or 
         receiver or codec capabilities.  The parameter MUST NOT be 
         present if the value of packetization-mode is equal to 0 or 1.  
         sprop-max-don-diff is an integer in the range of 0 to 32767, 
         inclusive.  If sprop-max-don-diff is not present, the value of 
         the parameter is unspecified.  sprop-max-don-diff is 
         calculated as follows: 

            sprop-max-don-diff = max{AbsDON(i) - AbsDON(j)}, 
            for any i and any j>i, 

         where i and j indicate the index of the NAL unit in the 
         transmission order and AbsDON denotes a decoding order number 
         of the NAL unit that does not wrap around to 0 after 65535.  
         In other words, AbsDON is calculated as follows: Let m and n 
         be consecutive NAL units in transmission order.  For the very 
 
 
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         first NAL unit in transmission order (whose index is 0), 
         AbsDON(0) = DON(0).  For other NAL units, AbsDON is calculated 
         as follows: 

            If DON(m) == DON(n), AbsDON(n) = AbsDON(m) 

            If (DON(m) < DON(n) and DON(n) - DON(m) < 32768), 
              AbsDON(n) = AbsDON(m) + DON(n) - DON(m) 

            If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768), 
              AbsDON(n) = AbsDON(m) + 65536 - DON(m) + DON(n) 

            If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768), 
              AbsDON(n) = AbsDON(m) - (DON(m) + 65536 - DON(n)) 

            If (DON(m) > DON(n) and DON(m) - DON(n) < 32768), 
              AbsDON(n) = AbsDON(m) - (DON(m) - DON(n)) 

         where DON(i) is the decoding order number of the NAL unit 
         having index i in the transmission order.  The decoding order 
         number is specified in section 5.5 of RFC 3984. 

            Informative note: Receivers may use sprop-max-don-diff to 
            trigger which NAL units in the receiver buffer can be 
            passed to the decoder. 

      max-rcmd-nalu-size: 
         This parameter MAY be used to signal the capabilities of a 
         receiver.  The parameter MUST NOT be used for any other 
         purposes.  The value of the parameter indicates the largest 
         NALU size in bytes that the receiver can handle efficiently.  
         The parameter value is a recommendation, not a strict upper 
         boundary.  The sender MAY create larger NALUs but must be 
         aware that the handling of these may come at a higher cost 
         than NALUs conforming to the limitation. 

         The value of max-rcmd-nalu-size MUST be an integer in the 
         range of 0 to 4294967295, inclusive.  If this parameter is not 
         specified, no known limitation to the NALU size exists.  
         Senders still have to consider the MTU size available between 
         the sender and the receiver and SHOULD run MTU discovery for 
         this purpose. 

         This parameter is motivated by, for example, an IP to H.223 
         video telephony gateway, where NALUs smaller than the H.223 
         transport data unit will be more efficient.  A gateway may 

 
 
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         terminate IP; thus, MTU discovery will normally not work 
         beyond the gateway. 

            Informative note: Setting this parameter to a lower than 
            necessary value may have a negative impact. 

      spatial-resolution: 
         This parameter MAY be used to indicate the maximum spatial 
         resolution of a NAL unit stream or the preferred spatial 
         resolution of a receiver.  The value is a base16 [6] 
         (hexadecimal) representation of the width and height of the 
         spatial resolution, in pixels, separated by a comma.  

      Encoding considerations: 
         This type is only defined for transfer via RTP (RFC 3550). 

      Security considerations: 
         See section 9 of RFC xxxx. 

      Public specification: 
         Please refer to RFC xxxx and its section 15. 

      Additional information: 
         None 

      File extensions:     none 

      Macintosh file type code: none 

      Object identifier or OID: none 

      Person & email address to contact for further information: 
         Ye-Kui Wang, ye-kui.wang@nokia.com 

      Intended usage:      COMMON 

      Author: 
         Ye-Kui Wang, ye-kui.wang@nokia.com 

      Change controller: 
         IETF Audio/Video Transport working group delegated from the 
         IESG. 





 
 
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8.2. SDP Parameters 

8.2.1. Mapping of MIME Parameters to SDP 

   The MIME media type video/H264 string is mapped to fields in the 
   Session Description Protocol (SDP) [5] as follows: 

   o  The media name in the "m=" line of SDP MUST be video. 

   o  The encoding name in the "a=rtpmap" line of SDP MUST be H264 (the 
      MIME subtype). 

   o  The clock rate in the "a=rtpmap" line MUST be 90000. 

   o  The OPTIONAL parameters "profile-level-id", "max-mbps", "max-fs", 
      "max-cpb", "max-dpb", "max-br", "redundant-pic-cap", "sprop-
      parameter-sets", "packetization-mode", "sprop-interleaving-depth", 
      "deint-buf-cap", "sprop-deint-buf-req", "sprop-init-buf-time", 
      "sprop-max-don-diff", "max-rcmd-nalu-size", and "spatial-
      resolution", when present, MUST be included in the "a=fmtp" line 
      of SDP.  These parameters are expressed as a MIME media type 
      string, in the form of a semicolon separated list of 
      parameter=value pairs. 

   An example of media representation in SDP is as follows (Baseline 
   Profile, Level 3.0, some of the constraints of the Main profile may 
   not be obeyed): 

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; 
                packetization-mode=1; 
                spatial-resolution=704,576; 
                sprop-parameter-sets=<base64 data> 

8.2.2. Usage with the SDP Offer/Answer Model 

   When H.264 is offered over RTP using SDP in an Offer/Answer model [7] 
   for negotiation for unicast usage, the following limitations and 
   rules apply: 







 
 
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   o  The parameters identifying a media format configuration for H.264 
      are "profile-level-id", "packetization-mode", and, if required by 
      "packetization-mode", "sprop-deint-buf-req".  These media format 
      configuration parameters (except for the level part of "profile-
      level-id") MUST be used symmetrically; i.e., the answerer MUST 
      either maintain all configuration parameters or remove the media 
      format (payload type) completely, if one or more of the parameter 
      values are not supported. For the level part of "profile-level-
      id", the answerer MUST maintain the same or a lower level or 
      remove the media format (payload type) completely.  

         Informative note: The requirement for symmetric use applies 
         only for the above media format configuration parameters and 
         not for the other stream properties and capability parameters, 
         including the level part of "profile-level-id". 

         Informative note: In H.264, all the levels except for level 1b 
         are equal to the value of level_idc divided by 10.  Level 1b 
         is a level higher than level 1.0 but lower than level 1.1, and 
         is signaled in an ad-hoc manner, due to that the level was 
         specified after level 1.0 and level 1.1.  For the Baseline, 
         Main and Extended profiles (with profile_idc equal to 66, 77 
         and 88, respectively), level 1b is indicated by level_idc 
         equal to 11 (i.e. same as level 1.1) and constraint_set3_flag 
         equal to 1.  For other profiles, level 1b is indicated by 
         level_idc equal to 9 (but note that level 1b for these 
         profiles are still higher than level 1, which has level_idc 
         equal to 10, and lower than level 1.1). 

      To simplify handling and matching of these configurations, the 
      same RTP payload type number used in the offer SHOULD also be 
      used in the answer, as specified in [7].  An answer MUST NOT 
      contain a payload type number used in the offer unless the 
      configuration ("profile-level-id", "packetization-mode", and, if 
      present, "sprop-deint-buf-req") is the same as in the offer or 
      the configuration only differs from that in the offer with a 
      lower level indicated by "profile-level-id". 

         Informative note: An offerer, when receiving the answer, has 
         to compare payload types not declared in the offer based on 
         media type (i.e., video/h264) and the above media format 
         configuration parameters with any payload types it has already 
         declared, in order to determine whether the configuration in 
         question is new or equivalent to a configuration already 
         offered. 


 
 
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   o  The parameters "packetization-mode", and if present, "sprop-deint-
      buf-req", "sprop-parameter-sets", "sprop-interleaving-depth", 
      "sprop-max-don-diff", and "sprop-init-buf-time", describe the 
      properties of the RTP packet stream that the offerer or answerer 
      is sending for this media format configuration.  This differs from 
      the normal usage of the Offer/Answer parameters: normally such 
      parameters declare the properties of the stream that the offerer 
      or the answerer is able to receive.  When dealing with H.264, the 
      offerer assumes that the answerer will be able to receive media 
      encoded using the configuration being offered. 

         Informative note: The above parameters apply for any stream 
         sent by the declaring entity with the same configuration; 
         i.e., they are dependent on their source.  Rather than being 
         bound to the payload type, the values may have to be applied 
         to another payload type when being sent, as they apply for the 
         configuration. 

   o  The capability parameters ("max-mbps", "max-fs", "max-cpb", "max-
      dpb", "max-br", ,"redundant-pic-cap", "max-rcmd-nalu-size") MAY be 
      used to declare further capabilities.  These parameters can only 
      be present when the direction attribute is sendrecv or recvonly, 
      and the parameters describe the limitations of what the receiver 
      accepts. 

   o  As specified above, an offerer has to include the size of the 
      deinterleaving buffer in the offer for an interleaved H.264 
      stream.  To enable the offerer and answerer to inform each other 
      about their capabilities for deinterleaving buffering, both 
      parties are RECOMMENDED to include "deint-buf-cap".  This 
      information MAY be used when the value for "sprop-deint-buf-req" 
      is selected in a second round of offer and answer.  For 
      interleaved streams, it is also RECOMMENDED to consider offering 
      multiple payload types with different buffering requirements when 
      the capabilities of the receiver are unknown. 

   For streams being delivered over multicast, the following rules 
   apply: 

   o  The media format configuration is identified by the same 
      parameters as above for unicast (i.e. "profile-level-id", 
      "packetization-mode", and, if required by "packetization-mode", 
      "sprop-deint-buf-req").  These media format configuration 
      parameters (including the level part of "profile-level-id") MUST 
      be used symmetrically; i.e., the answerer MUST either maintain all 
      configuration parameters or remove the media format (payload type) 
      completely.  
 
 
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   o  The stream properties parameters ("sprop-parameter-sets", "sprop-
      interleaving-depth", "sprop-max-don-diff", and "sprop-init-buf-
      time") MUST NOT be changed by the answerer.  Thus, a payload type 
      can either be accepted unaltered or removed. 

   o  The receiver capability parameters "max-mbps", "max-fs", "max-
      cpb", "max-dpb", "max-br", and "max-rcmd-nalu-size" MUST be 
      supported by the answerer for all streams declared as sendrecv or 
      recvonly; otherwise, one of the following actions MUST be 
      performed: the media format is removed, or the session rejected. 

   o  The receiver capability parameter redundant-pic-cap SHOULD be 
      supported by the answerer for all streams declared as sendrecv or 
      recvonly as follows:  The answerer SHOULD NOT include redundant 
      coded pictures in the transmitted stream if the offerer indicated 
      redundant-pic-cap equal to 0.  Otherwise (when redundant_pic_cap 
      is equal to 1), it is beyond the scope of this memo to recommend 
      how the answerer should use redundant coded pictures.   

   Below are the complete lists of how the different parameters shall be 
   interpreted in the different combinations of offer or answer and 
   direction attribute. 

   o  In offers and answers for which "a=sendrecv" or no direction 
      attribute is used, or in offers and answers for which "a=recvonly" 
      is used, the following interpretation of the parameters MUST be 
      used. 

      Declaring actual configuration or properties for receiving: 

         - profile-level-id 
         - packetization-mode 

      Declaring actual properties of the stream to be sent (applicable 
      only when "a=sendrecv" or no direction attribute is used): 

         - sprop-deint-buf-req 
         - sprop-interleaving-depth 
         - sprop-parameter-sets 
         - sprop-max-don-diff 
         - sprop-init-buf-time 
         - spatial-resolution 

         Informative note: When "a=sendrecv" or no direction attribute 
         is used, "spatial-resolution" indicates both the maximum 
         spatial resolution of the stream sent by the declaring entity 
         and the preferred spatial resolution for receiving a stream.  
 
 
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      Declaring receiver capabilities: 

         - max-mbps 
         - max-fs 
         - max-cpb 
         - max-dpb 
         - max-br 
         - redundant-pic-cap 
         - deint-buf-cap 
         - max-rcmd-nalu-size 

      Declaring receiver preference: 

         - spatial-resolution 

   o  In an offer or answer for which the direction attribute 
      "a=sendonly" is included for the media stream, the following 
      interpretation of the parameters MUST be used: 

      Declaring actual configuration and properties of stream proposed 
      to be sent: 

         - profile-level-id 
         - packetization-mode 
         - sprop-deint-buf-req 
         - sprop-max-don-diff 
         - sprop-init-buf-time 
         - sprop-parameter-sets 
         - sprop-interleaving-depth 
         - spatial-resolution 

   Furthermore, the following considerations are necessary: 

   o  Parameters used for declaring receiver capabilities are in general 
      downgradable; i.e., they express the upper limit for a sender's 
      possible behavior.  Thus a sender MAY select to set its encoder 
      using only lower/less or equal values of these parameters.  
      "sprop-parameter-sets" MUST NOT be used in a sender's declaration 
      of its capabilities, as the limits of the values that are carried 
      inside the parameter sets are implicit with the profile and level 
      used. 

   o  Parameters declaring a configuration point are not downgradable, 
      with the exception of the level part of the "profile-level-id" 
      parameter.  This expresses values a receiver expects to be used 
      and must be used verbatim on the sender side. 

 
 
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   o  When a sender's capabilities are declared, and non-downgradable 
      parameters are used in this declaration, then these parameters 
      express a configuration that is acceptable.  In order to achieve 
      high interoperability levels, it is often advisable to offer 
      multiple alternative configurations; e.g., for the packetization 
      mode.  It is impossible to offer multiple configurations in a 
      single payload type.  Thus, when multiple configuration offers are 
      made, each offer requires its own RTP payload type associated with 
      the offer. 

   o  A receiver SHOULD understand all MIME parameters, even if it only 
      supports a subset of the payload format's functionality.  This 
      ensures that a receiver is capable of understanding when an offer 
      to receive media can be downgraded to what is supported by the 
      receiver of the offer. 

   o  An answerer MAY extend the offer with additional media format 
      configurations.  However, to enable their usage, in most cases a 
      second offer is required from the offerer to provide the stream 
      properties parameters that the media sender will use.  This also 
      has the effect that the offerer has to be able to receive this 
      media format configuration, not only to send it. 

   o  If an offerer wishes to have non-symmetric capabilities between 
      sending and receiving, the offerer has to offer different RTP 
      sessions; i.e., different media lines declared as "recvonly" and 
      "sendonly", respectively.  This may have further implications on 
      the system. 

8.2.3. Usage in Declarative Session Descriptions 

   When H.264 over RTP is offered with SDP in a declarative style, as in 
   RTSP [27] or SAP [28], the following considerations are necessary. 

   o  All parameters capable of indicating the properties of both an RTP 
      packet stream and a receiver are used to indicate the properties 
      of an RTP packet stream.  For example, in this case, the parameter 
      "profile-level-id" declares the values used by the stream, instead 
      of the capabilities of the sender.  This results in that the 
      following interpretation of the parameters MUST be used: 

      Declaring actual configuration or stream properties: 

         - profile-level-id 
         - sprop-parameter-sets 
         - packetization-mode 
         - sprop-interleaving-depth 
 
 
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         - sprop-deint-buf-req 
         - sprop-max-don-diff 
         - sprop-init-buf-time 

      Not usable: 

         - max-mbps 
         - max-fs 
         - max-cpb 
         - max-dpb 
         - max-br 
         - redundant-pic-cap 
         - max-rcmd-nalu-size 
         - deint-buf-cap 

   o  A receiver of the SDP is required to support all parameters and 
      values of the parameters provided; otherwise, the receiver MUST 
      reject (RTSP) or not participate in (SAP) the session.  It falls 
      on the creator of the session to use values that are expected to 
      be supported by the receiving application. 

8.3. Examples 

   An SDP Offer/Answer exchange wherein both parties are expected to 
   both send and receive could look like the following.  Only the media 
   codec specific parts of the SDP are shown.  Some lines are wrapped 
   due to text constraints. 

      Offerer -> Answerer SDP message: 

      m=video 49170 RTP/AVP 100 99 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; packetization-mode=0; 
        sprop-parameter-sets=<base64 data#0> 
      a=rtpmap:99 H264/90000 
      a=fmtp:99 profile-level-id=42A01E; packetization-mode=1; 
        sprop-parameter-sets=<base64 data#1> 
      a=rtpmap:100 H264/90000 
      a=fmtp:100 profile-level-id=42A01E; packetization-mode=2; 
        sprop-parameter-sets=<base64 data#2>; 
        sprop-interleaving-depth=45; sprop-deint-buf-req=64000; 
        sprop-init-buf-time=102478; deint-buf-cap=128000 

   The above offer presents the same codec configuration in three 
   different packetization formats.  PT 98 represents single NALU mode, 
   PT 99 represents non-interleaved mode, and PT 100 indicates the 
   interleaved mode.  In the interleaved mode case, the interleaving 
 
 
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   parameters that the offerer would use if the answer indicates support 
   for PT 100 are also included.  In all three cases the parameter 
   "sprop-parameter-sets" conveys the initial parameter sets that are 
   required by the answerer when receiving a stream from the offerer 
   when this configuration (profile-level-id and packetization mode) is 
   accepted.  Note that the value for "sprop-parameter-sets" could be 
   different for each payload type. 

      Answerer -> Offerer SDP message: 

      m=video 49170 RTP/AVP 100 99 97 
      a=rtpmap:97 H264/90000 
      a=fmtp:97 profile-level-id=42A01E; packetization-mode=0; 
        sprop-parameter-sets=<base64 data#3> 
      a=rtpmap:99 H264/90000 
      a=fmtp:99 profile-level-id=42A01E; packetization-mode=1; 
        sprop-parameter-sets=<base64 data#4>;  
        max-rcmd-nalu-size=3980 
      a=rtpmap:100 H264/90000 
      a=fmtp:100 profile-level-id=42A01E; packetization-mode=2; 
        sprop-parameter-sets=<base64 data#5>;  
        sprop-interleaving-depth=60; 
        sprop-deint-buf-req=86000; sprop-init-buf-time=156320; 
        deint-buf-cap=128000; max-rcmd-nalu-size=3980 

   As the Offer/Answer negotiation covers both sending and receiving 
   streams, an offer indicates the exact parameters for what the offerer 
   is willing to receive, whereas the answer indicates the same for what 
   the answerer accepts to receive.  In this case the offerer declared 
   that it is willing to receive payload type 98.  The answerer accepts 
   this by declaring an equivalent payload type 97; i.e., it has 
   identical values for the two parameters "profile-level-id" and 
   "packetization-mode" (since "packetization-mode" is equal to 0, 
   "sprop-deint-buf-req" is not present).  As the offered payload type 
   98 is accepted, the answerer needs to store parameter sets included 
   in sprop-parameter-sets=<base64 data#0> in case the offer finally 
   decides to use this configuration. In the answer, the answerer 
   includes the parameter sets in sprop-parameter-sets=<base64 data#3> 
   that the answerer would use in the stream sent from the answerer if 
   this configuration is finally used.  

   The answerer also accepts the reception of the two configurations 
   that payload types 99 and 100 represent.  Again, the answerer needs 
   to store parameter sets included in sprop-parameter-sets=<base64 
   data#1> and sprop-parameter-sets=<base64 data#2> in case the offer 
   finally decides to use either of these two configurations.  The 
   answerer provides the initial parameter sets for the answerer-to-
 
 
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   offerer direction, i.e. the parameter sets in sprop-parameter-
   sets=<base64 data#4> and sprop-parameter-sets=<base64 data#5>, for 
   payload types 99 and 100, respectively, that it will use to send the 
   payload types.  The answerer also provides the offerer with its 
   memory limit for deinterleaving operations by providing a "deint-buf-
   cap" parameter.  This is only useful if the offerer decides on making 
   a second offer, where it can take the new value into account.  The 
   "max-rcmd-nalu-size" indicates that the answerer can efficiently 
   process NALUs up to the size of 3980 bytes.  However, there is no 
   guarantee that the network supports this size. 

   Below are some more examples. 

   In the following example, the original offer is accepted without 
   downgrading the level part of "profile-level-id", and "sprop-
   parameter-sets" is present (i.e. there is out-of-band transmission of 
   parameter sets).  This case needs only one round of offer/answer.  
   Note that sprop-parameter-sets=<base-64 data#0> is basically 
   independent of sprop-parameter-sets=<base-64 data#1>.  The former is 
   to be used by the encoder of the offerer and the decoder of the 
   answerer.  The latter is to be used by the encoder of the answerer 
   and the decoder of the offerer.  Note that requiring them (including 
   both sequence parameter sets and picture parameter sets) to be 
   identical or the former to be a subset of the latter would seriously 
   limit independent encoding optimizations by the independent encoders. 

      Offer SDP: 

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 
        spatial-resolution=704,576; 
        packetization-mode=1; 
        sprop-parameter-sets=<base-64 data#0>  

      Answer SDP:  

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 
        spatial-resolution=704,576; 
        packetization-mode=1; 
        sprop-parameter-sets=<base-64 data#1>  

   In the following example, the original offer is also accepted without 
   downgrading the level part of "profile-level-id", but "sprop-
   parameter-sets" is not present, meaning that there is no out-of-band 
 
 
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   transmission of parameter sets, which then have to be transmitted in-
   band.  This case also needs only one round of offer/answer. 

      Offer SDP:  

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 
        packetization-mode=1; 
        spatial-resolution=704,576 

      Answer SDP:  

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 
        packetization-mode=1; 
        spatial-resolution=704,576 

   In the following example, the original offer is accepted with 
   downgrading the level part of "profile-level-id", and "sprop-
   parameter-sets" is present (i.e. there is out-of-band transmission of 
   parameter sets).  This case needs at least two rounds of offer/answer 
   unless the offer includes multiple payload types for different 
   levels, which makes the SDP message larger.  The reason for the need 
   of more than one offer/answer round is because the "sprop-parameter-
   sets" in the original offer is not applicable to any level lower than 
   the one indicated by the level part of "profile-level-id".  

   Note that sprop-parameter-sets=<base-64 data#0> contains level_idc 
   indicating Level 3.0, therefore cannot be used as the answerer wants 
   Level 2.0 and does not need to be stored by the answerer. The sprop-
   parameter-sets=<base-64 data#2> is to be used by the encoder of the 
   offerer and the decoder of the answerer. The sprop-parameter-
   sets=<base-64 data#1> is to be used by the encoder of the answerer 
   and the decoder of the offerer.  

      Offer SDP:  

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 
        packetization-mode=1; 
        spatial-resolution=704,576; 
        sprop-parameter-sets=<base-64 data#0>  

      Answer SDP: 
 
 
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      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0 
        packetization-mode=1; 
        spatial-resolution=352,288; 
        sprop-parameter-sets=<base-64 data#1> 

      Offer SDP: 

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:97 profile-level-id=42A014; //Baseline profile, Level 2.0 
        packetization-mode=1; 
        spatial-resolution=352,288; 
        sprop-parameter-sets=<base-64 data#2> 

      Answer SDP: //This SDP is identical to previous answer SDP 

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0 
        packetization-mode=1; 
        spatial-resolution=352,288; 
        sprop-parameter-sets=<base-64 data#1> 

   In the following example, the original offer is also accepted with 
   downgrading the level part of "profile-level-id", but "sprop-
   parameter-sets" is not present, meaning that there is no out-of-band 
   transmission of parameter sets, which then have to be transmitted in-
   band.  This case also needs only one round of offer/answer. 

      Offer SDP:  

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A01E; //Baseline profile, Level 3.0 
        packetization-mode=1; 
        spatial-resolution=704,576 

      Answer SDP:  

      m=video 49170 RTP/AVP 98 
      a=rtpmap:98 H264/90000 
      a=fmtp:98 profile-level-id=42A014; //Baseline profile, Level 2.0 
        packetization-mode=1; 
        spatial-resolution=352,288; 

 
 
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8.4. Parameter Set Considerations 

   The H.264 parameter sets are a fundamental part of the video codec 
   and vital to its operation; see section 1.2.  Due to their 
   characteristics and their importance for the decoding process, lost 
   or erroneously transmitted parameter sets can hardly be concealed 
   locally at the receiver.  A reference to a corrupt parameter set has 
   normally fatal results to the decoding process.  Corruption could 
   occur, for example, due to the erroneous transmission or loss of a 
   parameter set data structure, but also due to the untimely 
   transmission of a parameter set update.  Therefore, the following 
   recommendations are provided as a guideline for the implementer of 
   the RTP sender. 

   Parameter set NALUs can be transported using three different 
   principles: 

   A. Using a session control protocol (out-of-band) prior to the actual 
     RTP session. 

   B. Using a session control protocol (out-of-band) during an ongoing 
     RTP session. 

   C. Within the RTP packet stream in the payload (in-band) during an 
     ongoing RTP session. 

   It is necessary to implement principles A and B within a session 
   control protocol.  SIP and SDP can be used as described in the SDP 
   Offer/Answer model and in the previous sections of this memo.  This 
   section contains guidelines on how principles A and B must be 
   implemented within session control protocols.  It is independent of 
   the particular protocol used.  Principle C is supported by the RTP 
   payload format defined in this specification. 

   The picture and sequence parameter set NALUs SHOULD NOT be 
   transmitted in the RTP payload unless reliable transport is provided 
   for RTP, as a loss of a parameter set of either type will likely 
   prevent decoding of a considerable portion of the corresponding RTP 
   packet stream.  Thus, the transmission of parameter sets using a 
   reliable session control protocol (i.e., usage of principle A or B 
   above) is RECOMMENDED. 

   In the rest of the section it is assumed that out-of-band signaling 
   provides reliable transport of parameter set NALUs and that in-band 
   transport does not.  If in-band signaling of parameter sets is used, 
   the sender SHOULD take the error characteristics into account and use 
   mechanisms to provide a high probability for delivering the parameter 
 
 
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   sets correctly.  Mechanisms that increase the probability for a 
   correct reception include packet repetition, FEC, and retransmission.  
   The use of an unreliable, out-of-band control protocol has similar 
   disadvantages as the in-band signaling (possible loss) and, in 
   addition, may also lead to difficulties in the synchronization (see 
   below).  Therefore, it is NOT RECOMMENDED. 

   Parameter sets MAY be added or updated during the lifetime of a 
   session using principles B and C.  It is required that parameter sets 
   are present at the decoder prior to the NAL units that refer to them.  
   Updating or adding of parameter sets can result in further problems, 
   and therefore the following recommendations should be considered. 

   - When parameter sets are added or updated, principle C is 
     vulnerable to transmission errors as described above, and 
     therefore principle B is RECOMMENDED. 

   - When parameter sets are added or updated, care SHOULD be taken to 
     ensure that any parameter set is delivered prior to its usage.  It 
     is common that no synchronization is present between out-of-band 
     signaling and in-band traffic.  If out-of-band signaling is used, 
     it is RECOMMENDED that a sender does not start sending NALUs 
     requiring the updated parameter sets prior to acknowledgement of 
     delivery from the signaling protocol. 

   - When parameter sets are updated, the following synchronization 
     issue should be taken into account.  When overwriting a parameter 
     set at the receiver, the sender has to ensure that the parameter 
     set in question is not needed by any NALU present in the network 
     or receiver buffers.  Otherwise, decoding with a wrong parameter 
     set may occur.  To lessen this problem, it is RECOMMENDED either 
     to overwrite only those parameter sets that have not been used for 
     a sufficiently long time (to ensure that all related NALUs have 
     been consumed), or to add a new parameter set instead (which may 
     have negative consequences for the efficiency of the video 
     coding). 

   - When new parameter sets are added, previously unused parameter set 
     identifiers are used.  This avoids the problem identified in the 
     previous paragraph.  However, in a multiparty session, unless a 
     synchronized control protocol is used, there is a risk that 
     multiple entities try to add different parameter sets for the same 
     identifier, which has to be avoided. 




 
 
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   - Adding or modifying parameter sets by using both principles B and 
     C in the same RTP session may lead to inconsistencies of the 
     parameter sets because of the lack of synchronization between the 
     control and the RTP channel.  Therefore, principles B and C MUST 
     NOT both be used in the same session unless sufficient 
     synchronization can be provided. 

   In some scenarios (e.g., when only the subset of this payload format 
   specification corresponding to H.241 is used), it is not possible to 
   employ out-of-band parameter set transmission.  In this case, 
   parameter sets have to be transmitted in-band.  Here, the 
   synchronization with the non-parameter-set-data in the bitstream is 
   implicit, but the possibility of a loss has to be taken into account.  
   The loss probability should be reduced using the mechanisms discussed 
   above. 

   - When parameter sets are initially provided using principle A and 
     then later added or updated in-band (principle C), there is a risk 
     associated with updating the parameter sets delivered out-of-band.  
     If receivers miss some in-band updates (for example, because of a 
     loss or a late tune-in), those receivers attempt to decode the 
     bitstream using out-dated parameters.  It is therefore RECOMMENDED 
     that parameter set IDs be partitioned between the out-of-band and 
     in-band parameter sets. 

9. Security Considerations 

   RTP packets using the payload format defined in this specification 
   are subject to the security considerations discussed in the RTP 
   specification [4], and in any appropriate RTP profile (for example, 
   [16]).  This implies that confidentiality of the media streams is 
   achieved by encryption; for example, through the application of SRTP 
   [26].  Because the data compression used with this payload format is 
   applied end-to-end, any encryption needs to be performed after 
   compression.  A potential denial-of-service threat exists for data 
   encodings using compression techniques that have non-uniform 
   receiver-end computational load.  The attacker can inject 
   pathological datagrams into the stream that are complex to decode and 
   that cause the receiver to be overloaded.  H.264 is particularly 
   vulnerable to such attacks, as it is extremely simple to generate 
   datagrams containing NAL units that affect the decoding process of 
   many future NAL units.  Therefore, the usage of data origin 
   authentication and data integrity protection of at least the RTP 
   packet is RECOMMENDED; for example, with SRTP [26]. 

   Note that the appropriate mechanism to ensure confidentiality and 
   integrity of RTP packets and their payloads is very dependent on the 
 
 
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   application and on the transport and signaling protocols employed.  
   Thus, although SRTP is given as an example above, other possible 
   choices exist. 

   Decoders MUST exercise caution with respect to the handling of user 
   data SEI messages, particularly if they contain active elements, and 
   MUST restrict their domain of applicability to the presentation 
   containing the stream. 

   End-to-End security with either authentication, integrity or 
   confidentiality protection will prevent a MANE from performing media-
   aware operations other than discarding complete packets.  And in the 
   case of confidentiality protection it will even be prevented from 
   performing discarding of packets in a media aware way.  To allow any 
   MANE to perform its operations, it will be required to be a trusted 
   entity which is included in the security context establishment. 

10. Congestion Control 

   Congestion control for RTP SHALL be used in accordance with RFC 3550 
   [4], and with any applicable RTP profile; e.g., RFC 3551 [16].  An 
   additional requirement if best-effort service is being used is: users 
   of this payload format MUST monitor packet loss to ensure that the 
   packet loss rate is within acceptable parameters.  Packet loss is 
   considered acceptable if a TCP flow across the same network path, and 
   experiencing the same network conditions, would achieve an average 
   throughput, measured on a reasonable timescale, that is not less than 
   the RTP flow is achieving.  This condition can be satisfied by 
   implementing congestion control mechanisms to adapt the transmission 
   rate (or the number of layers subscribed for a layered multicast 
   session), or by arranging for a receiver to leave the session if the 
   loss rate is unacceptably high. 

   The bit rate adaptation necessary for obeying the congestion control 
   principle is easily achievable when real-time encoding is used.  
   However, when pre-encoded content is being transmitted, bandwidth 
   adaptation requires the availability of more than one coded 
   representation of the same content, at different bit rates, or the 
   existence of non-reference pictures or sub-sequences [22] in the 
   bitstream.  The switching between the different representations can 
   normally be performed in the same RTP session; e.g., by employing a 
   concept known as SI/SP slices of the Extended Profile, or by 
   switching streams at IDR picture boundaries.  Only when non-
   downgradable parameters (such as the profile part of the 
   profile/level ID) are required to be changed does it become necessary 
   to terminate and re-start the media stream.  This may be accomplished 
   by using a different RTP payload type. 
 
 
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   MANEs MAY follow the suggestions outlined in section 7.3 and remove 
   certain unusable packets from the packet stream when that stream was 
   damaged due to previous packet losses.  This can help reduce the 
   network load in certain special cases. 

11. IANA Consideration 

   IANA has registered one new MIME type; see section 8.1. 

12. Informative Appendix: Application Examples 

   This payload specification is very flexible in its use, in order to 
   cover the extremely wide application space anticipated for H.264.  
   However, this great flexibility also makes it difficult for an 
   implementer to decide on a reasonable packetization scheme.  Some 
   information on how to apply this specification to real-world 
   scenarios is likely to appear in the form of academic publications 
   and a test model software and description in the near future.  
   However, some preliminary usage scenarios are described here as well. 

12.1. Video Telephony according to ITU-T Recommendation H.241 Annex A 

   H.323-based video telephony systems that use H.264 as an optional 
   video compression scheme are required to support H.241 Annex A [15] 
   as a packetization scheme.  The packetization mechanism defined in 
   this Annex is technically identical with a small subset of this 
   specification. 

   When a system operates according to H.241 Annex A, parameter set NAL 
   units are sent in-band.  Only Single NAL unit packets are used.  Many 
   such systems are not sending IDR pictures regularly, but only when 
   required by user interaction or by control protocol means; e.g., when 
   switching between video channels in a Multipoint Control Unit or for 
   error recovery requested by feedback. 

12.2. Video Telephony, No Slice Data Partitioning, No NAL Unit 
   Aggregation 

   The RTP part of this scheme is implemented and tested (though not the 
   control-protocol part; see below). 

   In most real-world video telephony applications, picture parameters 
   such as picture size or optional modes never change during the 
   lifetime of a connection.  Therefore, all necessary parameter sets 
   (usually only one) are sent as a side effect of the capability 
   exchange/announcement process, e.g., according to the SDP syntax 
   specified in section 8.2 of this document.  As all necessary 
 
 
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   parameter set information is established before the RTP session 
   starts, there is no need for sending any parameter set NAL units.  
   Slice data partitioning is not used, either.  Thus, the RTP packet 
   stream basically consists of NAL units that carry single coded 
   slices. 

   The encoder chooses the size of coded slice NAL units so that they 
   offer the best performance.  Often, this is done by adapting the 
   coded slice size to the MTU size of the IP network.  For small 
   picture sizes, this may result in a one-picture-per-one-packet 
   strategy.  Intra refresh algorithms clean up the loss of packets and 
   the resulting drift-related artifacts. 

12.3. Video Telephony, Interleaved Packetization Using NAL Unit 
   Aggregation 

   This scheme allows better error concealment and is used in H.263 
   based designs using RFC 2429 packetization [10].  It has been 
   implemented, and good results were reported [12]. 

   The VCL encoder codes the source picture so that all macroblocks 
   (MBs) of one MB line are assigned to one slice.  All slices with even 
   MB row addresses are combined into one STAP, and all slices with odd 
   MB row addresses into another.  Those STAPs are transmitted as RTP 
   packets.  The establishment of the parameter sets is performed as 
   discussed above. 

   Note that the use of STAPs is essential here, as the high number of 
   individual slices (18 for a CIF picture) would lead to unacceptably 
   high IP/UDP/RTP header overhead (unless the source coding tool FMO is 
   used, which is not assumed in this scenario).  Furthermore, some 
   wireless video transmission systems, such as H.324M and the IP-based 
   video telephony specified in 3GPP, are likely to use relatively small 
   transport packet size.  For example, a typical MTU size of H.223 AL3 
   SDU is around 100 bytes [17].  Coding individual slices according to 
   this packetization scheme provides further advantage in communication 
   between wired and wireless networks, as individual slices are likely 
   to be smaller than the preferred maximum packet size of wireless 
   systems.  Consequently, a gateway can convert the STAPs used in a 
   wired network into several RTP packets with only one NAL unit, which 
   are preferred in a wireless network, and vice versa. 

12.4. Video Telephony with Data Partitioning 

   This scheme has been implemented and has been shown to offer good 
   performance, especially at higher packet loss rates [12]. 

 
 
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   Data Partitioning is known to be useful only when some form of 
   unequal error protection is available.  Normally, in single-session 
   RTP environments, even error characteristics are assumed; i.e., the 
   packet loss probability of all packets of the session is the same 
   statistically.  However, there are means to reduce the packet loss 
   probability of individual packets in an RTP session.  A FEC packet 
   according to RFC 2733 [18], for example, specifies which media 
   packets are associated with the FEC packet. 

   In all cases, the incurred overhead is substantial but is in the same 
   order of magnitude as the number of bits that have otherwise been 
   spent for intra information.  However, this mechanism does not add 
   any delay to the system. 

   Again, the complete parameter set establishment is performed through 
   control protocol means. 

12.5. Video Telephony or Streaming with FUs and Forward Error Correction 

   This scheme has been implemented and has been shown to provide good 
   performance, especially at higher packet loss rates [19]. 

   The most efficient means to combat packet losses for scenarios where 
   retransmissions are not applicable is forward error correction (FEC).  
   Although application layer, end-to-end use of FEC is often less 
   efficient than an FEC-based protection of individual links 
   (especially when links of different characteristics are in the 
   transmission path), application layer, end-to-end FEC is unavoidable 
   in some scenarios.  RFC 2733 [18] provides means to use generic, 
   application layer, end-to-end FEC in packet-loss environments.  A 
   binary forward error correcting code is generated by applying the XOR 
   operation to the bits at the same bit position in different packets.  
   The binary code can be specified by the parameters (n,k) in which k 
   is the number of information packets used in the connection and n is 
   the total number of packets generated for k information packets; 
   i.e., n-k parity packets are generated for k information packets. 

   When a code is used with parameters (n,k) within the RFC 2733 
   framework, the following properties are well known: 

   a) If applied over one RTP packet, RFC 2733 provides only packet 
     repetition. 

   b) RFC 2733 is most bit rate efficient if XOR-connected packets have 
     equal length. 


 
 
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   c) At the same packet loss probability p and for a fixed k, the 
     greater the value of n is, the smaller the residual error 
     probability becomes.  For example, for a packet loss probability 
     of 10%, k=1, and n=2, the residual error probability is about 1%, 
     whereas for n=3, the residual error probability is about 0.1%. 

   d) At the same packet loss probability p and for a fixed code rate 
     k/n, the greater the value of n is, the smaller the residual error 
     probability becomes.  For example, at a packet loss probability of 
     p=10%, k=1 and n=2, the residual error rate is about 1%, whereas 
     for an extended Golay code with k=12 and n=24, the residual error 
     rate is about 0.01%. 

   For applying RFC 2733 in combination with H.264 baseline coded video 
   without using FUs, several options might be considered: 

   1) The video encoder produces NAL units for which each video frame is 
     coded in a single slice.  Applying FEC, one could use a simple 
     code; e.g., (n=2, k=1).  That is, each NAL unit would basically 
     just be repeated.  The disadvantage is obviously the bad code 
     performance according to d), above, and the low flexibility, as 
     only (n, k=1) codes can be used. 

   2) The video encoder produces NAL units for which each video frame is 
     encoded in one or more consecutive slices.  Applying FEC, one 
     could use a better code, e.g., (n=24, k=12), over a sequence of 
     NAL units.  Depending on the number of RTP packets per frame, a 
     loss may introduce a significant delay, which is reduced when more 
     RTP packets are used per frame.  Packets of completely different 
     length might also be connected, which decreases bit rate 
     efficiency according to b), above.  However, with some care and 
     for slices of 1kb or larger, similar length (100-200 bytes 
     difference) may be produced, which will not lower the bit 
     efficiency catastrophically. 

   3) The video encoder produces NAL units, for which a certain frame 
     contains k slices of possibly almost equal length.  Then, applying 
     FEC, a better code, e.g., (n=24, k=12), can be used over the 
     sequence of NAL units for each frame.  The delay compared to that 
     of 2), above,  may be reduced, but several disadvantages are 
     obvious.  First, the coding efficiency of the encoded video is 
     lowered significantly, as slice-structured coding reduces intra-
     frame prediction and additional slice overhead is necessary.  
     Second, pre-encoded content or, when operating over a gateway, the 
     video is usually not appropriately coded with k slices such that 
     FEC can be applied.  Finally, the encoding of video producing k 

 
 
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     slices of equal length is not straightforward and might require 
     more than one encoding pass. 

   Many of the mentioned disadvantages can be avoided by applying FUs in 
   combination with FEC.  Each NAL unit can be split into any number of 
   FUs of basically equal length; therefore, FEC with a reasonable k and 
   n can be applied, even if the encoder made no effort to produce 
   slices of equal length.  For example, a coded slice NAL unit 
   containing an entire frame can be split to k FUs, and a parity check 
   code (n=k+1, k) can be applied.  However, this has the disadvantage 
   that unless all created fragments can be recovered, the whole slice 
   will be lost.  Thus a larger section is lost than would be if the 
   frame had been split into several slices. 

   The presented technique makes it possible to achieve good 
   transmission error tolerance, even if no additional source coding 
   layer redundancy (such as periodic intra frames) is present.  
   Consequently, the same coded video sequence can be used to achieve 
   the maximum compression efficiency and quality over error-free 
   transmission and for transmission over error-prone networks.  
   Furthermore, the technique allows the application of FEC to pre-
   encoded sequences without adding delay.  In this case, pre-encoded 
   sequences that are not encoded for error-prone networks can still be 
   transmitted almost reliably without adding extensive delays.  In 
   addition, FUs of equal length result in a bit rate efficient use of 
   RFC 2733. 

   If the error probability depends on the length of the transmitted 
   packet (e.g., in case of mobile transmission [14]), the benefits of 
   applying FUs with FEC are even more obvious.  Basically, the 
   flexibility of the size of FUs allows appropriate FEC to be applied 
   for each NAL unit and unequal error protection of NAL units. 

   When FUs and FEC are used, the incurred overhead is substantial but 
   is in the same order of magnitude as the number of bits that have to 
   be spent for intra-coded macroblocks if no FEC is applied.  In [19], 
   it was shown that the overall performance of the FEC-based approach 
   enhanced quality when using the same error rate and same overall bit 
   rate, including the overhead. 

12.6. Low Bit-Rate Streaming 

   This scheme has been implemented with H.263 and non-standard RTP 
   packetization and has given good results [20].  There is no technical 
   reason why similarly good results could not be achievable with H.264. 


 
 
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   In today's Internet streaming, some of the offered bit rates are 
   relatively low in order to allow terminals with dial-up modems to 
   access the content.  In wired IP networks, relatively large packets, 
   say 500 - 1500 bytes, are preferred to smaller and more frequently 
   occurring packets in order to reduce network congestion.  Moreover, 
   use of large packets decreases the amount of RTP/UDP/IP header 
   overhead.  For low bit-rate video, the use of large packets means 
   that sometimes up to few pictures should be encapsulated in one 
   packet. 

   However, loss of a packet including many coded pictures would have 
   drastic consequences for visual quality, as there is practically no 
   other way to conceal a loss of an entire picture than to repeat the 
   previous one.  One way to construct relatively large packets and 
   maintain possibilities for successful loss concealment is to 
   construct MTAPs that contain interleaved slices from several 
   pictures.  An MTAP should not contain spatially adjacent slices from 
   the same picture or spatially overlapping slices from any picture.  
   If a packet is lost, it is likely that a lost slice is surrounded by 
   spatially adjacent slices of the same picture and spatially 
   corresponding slices of the temporally previous and succeeding 
   pictures.  Consequently, concealment of the lost slice is likely to 
   be relatively successful. 

12.7. Robust Packet Scheduling in Video Streaming 

   Robust packet scheduling has been implemented with MPEG-4 Part 2 and 
   simulated in a wireless streaming environment [21].  There is no 
   technical reason why similar or better results could not be 
   achievable with H.264. 

   Streaming clients typically have a receiver buffer that is capable of 
   storing a relatively large amount of data.  Initially, when a 
   streaming session is established, a client does not start playing the 
   stream back immediately.  Rather, it typically buffers the incoming 
   data for a few seconds.  This buffering helps maintain continuous 
   playback, as, in case of occasional increased transmission delays or 
   network throughput drops, the client can decode and play buffered 
   data.  Otherwise, without initial buffering, the client has to freeze 
   the display, stop decoding, and wait for incoming data.  The 
   buffering is also necessary for either automatic or selective 
   retransmission in any protocol level.  If any part of a picture is 
   lost, a retransmission mechanism may be used to resend the lost data.  
   If the retransmitted data is received before its scheduled decoding 
   or playback time, the loss is recovered perfectly.  Coded pictures 
   can be ranked according to their importance in the subjective quality 
   of the decoded sequence.  For example, non-reference pictures, such 
 
 
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   as conventional B pictures, are subjectively least important, as 
   their absence does not affect decoding of any other pictures.  In 
   addition to non-reference pictures, the ITU-T H.264 | ISO/IEC 14496-
   10 standard includes a temporal scalability method called sub-
   sequences [22].  Subjective ranking can also be made on coded slice 
   data partition or slice group basis.  Coded slices and coded slice 
   data partitions that are subjectively the most important can be sent 
   earlier than their decoding order indicates, whereas coded slices and 
   coded slice data partitions that are subjectively the least important 
   can be sent later than their natural coding order indicates.  
   Consequently, any retransmitted parts of the most important slices 
   and coded slice data partitions are more likely to be received before 
   their scheduled decoding or playback time compared to the least 
   important slices and slice data partitions. 

13. Informative Appendix: Rationale for Decoding Order Number 

13.1. Introduction 

   The Decoding Order Number (DON) concept was introduced mainly to 
   enable efficient multi-picture slice interleaving (see section 12.6) 
   and robust packet scheduling (see section 12.7).  In both of these 
   applications, NAL units are transmitted out of decoding order.  DON 
   indicates the decoding order of NAL units and should be used in the 
   receiver to recover the decoding order.  Example use cases for 
   efficient multi-picture slice interleaving and for robust packet 
   scheduling are given in sections 13.2 and 13.3, respectively.  
   Section 13.4 describes the benefits of the DON concept in error 
   resiliency achieved by redundant coded pictures.  Section 13.5 
   summarizes considered alternatives to DON and justifies why DON was 
   chosen to this RTP payload specification. 

13.2. Example of Multi-Picture Slice Interleaving 

   An example of multi-picture slice interleaving follows.  A subset of 
   a coded video sequence is depicted below in output order.  R denotes 
   a reference picture, N denotes a non-reference picture, and the 
   number indicates a relative output time. 

      ... R1 N2 R3 N4 R5 ... 

   The decoding order of these pictures from left to right is as 
   follows: 

      ... R1 R3 N2 R5 N4 ... 


 
 
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   The NAL units of pictures R1, R3, N2, R5, and N4 are marked with a 
   DON equal to 1, 2, 3, 4, and 5, respectively. 

   Each reference picture consists of three slice groups that are 
   scattered as follows (a number denotes the slice group number for 
   each macroblock in a QCIF frame): 

      0 1 2 0 1 2 0 1 2 0 1 
      2 0 1 2 0 1 2 0 1 2 0 
      1 2 0 1 2 0 1 2 0 1 2 
      0 1 2 0 1 2 0 1 2 0 1 
      2 0 1 2 0 1 2 0 1 2 0 
      1 2 0 1 2 0 1 2 0 1 2 
      0 1 2 0 1 2 0 1 2 0 1 
      2 0 1 2 0 1 2 0 1 2 0 
      1 2 0 1 2 0 1 2 0 1 2 

   For the sake of simplicity, we assume that all the macroblocks of a 
   slice group are included in one slice.  Three MTAPs are constructed 
   from three consecutive reference pictures so that each MTAP contains 
   three aggregation units, each of which contains all the macroblocks 
   from one slice group.  The first MTAP contains slice group 0 of 
   picture R1, slice group 1 of picture R3, and slice group 2 of picture 
   R5.  The second MTAP contains slice group 1 of picture R1, slice 
   group 2 of picture R3, and slice group 0 of picture R5.  The third 
   MTAP contains slice group 2 of picture R1, slice group 0 of picture 
   R3, and slice group 1 of picture R5.  Each non-reference picture is 
   encapsulated into an STAP-B. 

   Consequently, the transmission order of NAL units is the following:  

      R1, slice group 0, DON 1, carried in MTAP,RTP SN: N 
      R3, slice group 1, DON 2, carried in MTAP,RTP SN: N 
      R5, slice group 2, DON 4, carried in MTAP,RTP SN: N 
      R1, slice group 1, DON 1, carried in MTAP,RTP SN: N+1 
      R3, slice group 2, DON 2, carried in MTAP,RTP SN: N+1 
      R5, slice group 0, DON 4, carried in MTAP,RTP SN: N+1 
      R1, slice group 2, DON 1, carried in MTAP,RTP SN: N+2 
      R3, slice group 1, DON 2, carried in MTAP,RTP SN: N+2 
      R5, slice group 0, DON 4, carried in MTAP,RTP SN: N+2 
      N2, DON 3, carried in STAP-B, RTP SN: N+3 
      N4, DON 5, carried in STAP-B, RTP SN: N+4 

   The receiver is able to organize the NAL units back in decoding order 
   based on the value of DON associated with each NAL unit. 


 
 
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   If one of the MTAPs is lost, the spatially adjacent and temporally 
   co-located macroblocks are received and can be used to conceal the 
   loss efficiently.  If one of the STAPs is lost, the effect of the 
   loss does not propagate temporally. 

13.3. Example of Robust Packet Scheduling 

   An example of robust packet scheduling follows.  The communication 
   system used in the example consists of the following components in 
   the order that the video is processed from source to sink: 

      o camera and capturing 
      o pre-encoding buffer 
      o encoder 
      o encoded picture buffer 
      o transmitter 
      o transmission channel 
      o receiver 
      o receiver buffer 
      o decoder 
      o decoded picture buffer 
      o display 

   The video communication system used in the example operates as 
   follows.  Note that processing of the video stream happens gradually 
   and at the same time in all components of the system.  The source 
   video sequence is shot and captured to a pre-encoding buffer.  The 
   pre-encoding buffer can be used to order pictures from sampling order 
   to encoding order or to analyze multiple uncompressed frames for bit 
   rate control purposes, for example.  In some cases, the pre-encoding 
   buffer may not exist; instead, the sampled pictures are encoded right 
   away.  The encoder encodes pictures from the pre-encoding buffer and 
   stores the output; i.e., coded pictures, to the encoded picture 
   buffer.  The transmitter encapsulates the coded pictures from the 
   encoded picture buffer to transmission packets and sends them to a 
   receiver through a transmission channel.  The receiver stores the 
   received packets to the receiver buffer.  The receiver buffering 
   process typically includes buffering for transmission delay jitter.  
   The receiver buffer can also be used to recover correct decoding 
   order of coded data.  The decoder reads coded data from the receiver 
   buffer and produces decoded pictures as output into the decoded 
   picture buffer.  The decoded picture buffer is used to recover the 
   output (or display) order of pictures.  Finally, pictures are 
   displayed. 

   In the following example figures, I denotes an IDR picture, R denotes 
   a reference picture, N denotes a non-reference picture, and the 
 
 
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   number after I, R, or N indicates the sampling time relative to the 
   previous IDR picture in decoding order.  Values below the sequence of 
   pictures indicate scaled system clock timestamps.  The system clock 
   is initialized arbitrarily in this example, and time runs from left 
   to right.  Each I, R, and N picture is mapped into the same timeline 
   compared to the previous processing step, if any, assuming that 
   encoding, transmission, and decoding take no time.  Thus, events 
   happening at the same time are located in the same column throughout 
   all example figures. 

   A subset of a sequence of coded pictures is depicted below in 
   sampling order. 

       ...  N58 N59 I00 N01 N02 R03 N04 N05 R06 ... N58 N59 I00 N01 ... 
       ... --|---|---|---|---|---|---|---|---|- ... -|---|---|---|- ... 
       ...  58  59  60  61  62  63  64  65  66  ... 128 129 130 131 ... 

             Figure 16  Sequence of pictures in sampling order 

   The sampled pictures are buffered in the pre-encoding buffer to 
   arrange them in encoding order.  In this example, we assume that the 
   non-reference pictures are predicted from both the previous and the 
   next reference picture in output order, except for the non-reference 
   pictures immediately preceding an IDR picture, which are predicted 
   only from the previous reference picture in output order.  Thus, the 
   pre-encoding buffer has to contain at least two pictures, and the 
   buffering causes a delay of two picture intervals.  The output of the 
   pre-encoding buffering process and the encoding (and decoding) order 
   of the pictures are as follows: 

       ... N58 N59 I00 R03 N01 N02 R06 N04 N05 ... 
       ... -|---|---|---|---|---|---|---|---|- ... 
       ... 60  61  62  63  64  65  66  67  68  ... 

         Figure 17  Re-ordered pictures in the pre-encoding buffer 

   The encoder or the transmitter can set the value of DON for each 
   picture to a value of DON for the previous picture in decoding order 
   plus one. 

   For the sake of simplicity, let us assume that: 

   o  the frame rate of the sequence is constant, 
   o  each picture consists of only one slice, 
   o  each slice is encapsulated in a single NAL unit packet, 
   o  there is no transmission delay, and 

 
 
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   o  pictures are transmitted at constant intervals (that is, 1 / 
   (frame rate)). 

   When pictures are transmitted in decoding order, they are received as 
   follows: 

       ... N58 N59 I00 R03 N01 N02 R06 N04 N05 ... 
       ... -|---|---|---|---|---|---|---|---|- ... 
       ... 60  61  62  63  64  65  66  67  68  ... 

              Figure 18  Received pictures in decoding order 

   The OPTIONAL sprop-interleaving-depth MIME type parameter is set to 
   0, as the transmission (or reception) order is identical to the 
   decoding order. 

   The decoder has to buffer for one picture interval initially in its 
   decoded picture buffer to organize pictures from decoding order to 
   output order as depicted below: 

        ... N58 N59 I00 N01 N02 R03 N04 N05 R06 ... 
        ... -|---|---|---|---|---|---|---|---|- ... 
        ... 61  62  63  64  65  66  67  68  69  ... 

                          Figure 19  Output order 

   The amount of required initial buffering in the decoded picture 
   buffer can be signaled in the buffering period SEI message or with 
   the num_reorder_frames syntax element of H.264 video usability 
   information.  num_reorder_frames indicates the maximum number of 
   frames, complementary field pairs, or non-paired fields that precede 
   any frame, complementary field pair, or non-paired field in the 
   sequence in decoding order and that follow it in output order.  For 
   the sake of simplicity, we assume that num_reorder_frames is used to 
   indicate the initial buffer in the decoded picture buffer.  In this 
   example, num_reorder_frames is equal to 1. 

   It can be observed that if the IDR picture I00 is lost during 
   transmission and a retransmission request is issued when the value of 
   the system clock is 62, there is one picture interval of time (until 
   the system clock reaches timestamp 63) to receive the retransmitted 
   IDR picture I00. 

   Let us then assume that IDR pictures are transmitted two frame 
   intervals earlier than their decoding position; i.e., the pictures 
   are transmitted as follows: 

 
 
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        ...  I00 N58 N59 R03 N01 N02 R06 N04 N05 ... 
        ... --|---|---|---|---|---|---|---|---|- ... 
        ...  62  63  64  65  66  67  68  69  70  ... 

       Figure 20  Interleaving: Early IDR pictures in sending order 

   The OPTIONAL sprop-interleaving-depth MIME type parameter is set 
   equal to 1 according to its definition.  (The value of sprop-
   interleaving-depth in this example can be derived as follows: Picture 
   I00 is the only picture preceding picture N58 or N59 in transmission 
   order and following it in decoding order.  Except for pictures I00, 
   N58, and N59, the transmission order is the same as the decoding 
   order of pictures.  As a coded picture is encapsulated into exactly 
   one NAL unit, the value of sprop-interleaving-depth is equal to the 
   maximum number of pictures preceding any picture in transmission 
   order and following the picture in decoding order.) 

   The receiver buffering process contains two pictures at a time 
   according to the value of the sprop-interleaving-depth parameter and 
   orders pictures from the reception order to the correct decoding 
   order based on the value of DON associated with each picture.  The 
   output of the receiver buffering process is as follows: 

       ... N58 N59 I00 R03 N01 N02 R06 N04 N05 ... 
       ... -|---|---|---|---|---|---|---|---|- ... 
       ... 63  64  65  66  67  68  69  70  71  ... 

                 Figure 21  Interleaving: Receiver buffer 

   Again, an initial buffering delay of one picture interval is needed 
   to organize pictures from decoding order to output order, as depicted 
   below: 

        ... N58 N59 I00 N01 N02 R03 N04 N05 ... 
        ... -|---|---|---|---|---|---|---|- ... 
        ... 64  65  66  67  68  69  70  71  ... 

         Figure 22  Interleaving: Receiver buffer after reordering 

   Note that the maximum delay that IDR pictures can undergo during 
   transmission, including possible application, transport, or link 
   layer retransmission, is equal to three picture intervals.  Thus, the 
   loss resiliency of IDR pictures is improved in systems supporting 
   retransmission compared to the case in which pictures were 
   transmitted in their decoding order. 


 
 
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13.4. Robust Transmission Scheduling of Redundant Coded Slices 

   A redundant coded picture is a coded representation of a picture or a 
   part of a picture that is not used in the decoding process if the 
   corresponding primary coded picture is correctly decoded.  There 
   should be no noticeable difference between any area of the decoded 
   primary picture and a corresponding area that would result from 
   application of the H.264 decoding process for any redundant picture 
   in the same access unit.  A redundant coded slice is a coded slice 
   that is a part of a redundant coded picture. 

   Redundant coded pictures can be used to provide unequal error 
   protection in error-prone video transmission.  If a primary coded 
   representation of a picture is decoded incorrectly, a corresponding 
   redundant coded picture can be decoded.  Examples of applications and 
   coding techniques using the redundant codec picture feature include 
   the video redundancy coding [23] and the protection of "key pictures" 
   in multicast streaming [24]. 

   One property of many error-prone video communications systems is that 
   transmission errors are often bursty.  Therefore, they may affect 
   more than one consecutive transmission packets in transmission order.  
   In low bit-rate video communication, it is relatively common that an 
   entire coded picture can be encapsulated into one transmission 
   packet.  Consequently, a primary coded picture and the corresponding 
   redundant coded pictures may be transmitted in consecutive packets in 
   transmission order.  To make the transmission scheme more tolerant of 
   bursty transmission errors, it is beneficial to transmit the primary 
   coded picture and redundant coded picture separated by more than a 
   single packet.  The DON concept enables this. 

13.5. Remarks on Other Design Possibilities 

   The slice header syntax structure of the H.264 coding standard 
   contains the frame_num syntax element that can indicate the decoding 
   order of coded frames.  However, the usage of the frame_num syntax 
   element is not feasible or desirable to recover the decoding order, 
   due to the following reasons: 

   o  The receiver is required to parse at least one slice header per 
      coded picture (before passing the coded data to the decoder). 

   o  Coded slices from multiple coded video sequences cannot be 
      interleaved, as the frame number syntax element is reset to 0 in 
      each IDR picture. 


 
 
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   o  The coded fields of a complementary field pair share the same 
      value of the frame_num syntax element.  Thus, the decoding order 
      of the coded fields of a complementary field pair cannot be 
      recovered based on the frame_num syntax element or any other 
      syntax element of the H.264 coding syntax. 

   The RTP payload format for transport of MPEG-4 elementary streams 
   [25] enables interleaving of access units and transmission of 
   multiple access units in the same RTP packet.  An access unit is 
   specified in the H.264 coding standard to comprise all NAL units 
   associated with a primary coded picture according to subclause 
   7.4.1.2 of [1].  Consequently, slices of different pictures cannot be 
   interleaved, and the multi-picture slice interleaving technique (see 
   section 12.6) for improved error resilience cannot be used. 

14. Acknowledgements 

   The authors thank Roni Even, Dave Lindbergh, Philippe Gentric, 
   Gonzalo Camarillo, Gary Sullivan, Joerg Ott, and Colin Perkins for 
   careful review. 

   This document was prepared using 2-Word-v2.0.template.dot. 

15. References 

15.1. Normative References 

   [1]   ITU-T Recommendation H.264, "Advanced video coding for generic 
         audiovisual services", May 2003. 

   [2]   ISO/IEC International Standard 14496-10:2003. 

   [3]   Bradner, S., "Key words for use in RFCs to Indicate Requirement 
         Levels", BCP 14, RFC 2119, March 1997. 

   [4]   Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, 
         "RTP: A Transport Protocol for Real-Time Applications", STD 64, 
         RFC 3550, July 2003. 

   [5]   Handley, M. and V. Jacobson, "SDP: Session Description 
         Protocol", RFC 2327, April 1998. 

   [6]   Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", 
         RFC 3548, July 2003. 

   [7]   Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with 
         Session Description Protocol (SDP)", RFC 3264, June 2002. 
 
 
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15.2. Informative References 

   [8]   "Draft ITU-T Recommendation and Final Draft International 
         Standard of Joint Video Specification (ITU-T Rec. H.264 | 
         ISO/IEC 14496-10 AVC)", available from http://ftp3.itu.int/av-
         arch/jvt-site/2003_03_Pattaya/JVT-G050r1.zip, May 2003. 

   [9]   Luthra, A., Sullivan, G.J., and T. Wiegand (eds.), Special 
         Issue on H.264/AVC. IEEE Transactions on Circuits and Systems 
         on Video Technology, July 2003. 

   [10]  Bormann, C., Cline, L., Deisher, G., Gardos, T., Maciocco, C., 
         Newell, D., Ott, J., Sullivan, G., Wenger, S., and C. Zhu, "RTP 
         Payload Format for the 1998 Version of ITU-T Rec. H.263 Video 
         (H.263+)", RFC 2429, October 1998. 

   [11]  ISO/IEC IS 14496-2. 

   [12]  Wenger, S., "H.26L over IP", IEEE Transaction on Circuits and 
         Systems for Video technology, Vol. 13, No. 7, July 2003. 

   [13]  Wenger, S., "H.26L over IP: The IP Network Adaptation Layer", 
         Proceedings Packet Video Workshop 02, April 2002. 

   [14]  Stockhammer, T., Hannuksela, M.M., and S. Wenger, "H.26L/JVT 
         Coding Network Abstraction Layer and IP-based Transport" in 
         Proc. ICIP 2002, Rochester, NY, September 2002. 

   [15]  ITU-T Recommendation H.241, "Extended video procedures and 
         control signals for H.300 series terminals", 2004. 

   [16]  Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video 
         Conferences with Minimal Control", STD 65, RFC 3551, July 2003. 

   [17]  ITU-T Recommendation H.223, "Multiplexing protocol for low bit 
         rate multimedia communication", July 2001. 

   [18]  Rosenberg, J. and H. Schulzrinne, "An RTP Payload Format for 
         Generic Forward Error Correction", RFC 2733, December 1999. 

   [19]  Stockhammer, T., Wiegand, T., Oelbaum, T., and F. Obermeier, 
         "Video Coding and Transport Layer Techniques for H.264/AVC-
         Based Transmission over Packet-Lossy Networks", IEEE 
         International Conference on Image Processing (ICIP 2003), 
         Barcelona, Spain, September 2003. 


 
 
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   [20]  Varsa, V. and M. Karczewicz, "Slice interleaving in compressed 
         video packetization", Packet Video Workshop 2000. 

   [21]  Kang, S.H. and A. Zakhor, "Packet scheduling algorithm for 
         wireless video streaming," International Packet Video Workshop 
         2002. 

   [22]  Hannuksela, M.M., "Enhanced concept of GOP", JVT-B042, 
         available http://ftp3.itu.int/av-arch/video-site/0201_Gen/JVT-
         B042.doc, anuary 2002. 

   [23]  Wenger, S., "Video Redundancy Coding in H.263+", 1997 
         International Workshop on Audio-Visual Services over Packet 
         Networks, September 1997. 

   [24]  Wang, Y.-K., Hannuksela, M.M., and M. Gabbouj, "Error Resilient 
         Video Coding Using Unequally Protected Key Pictures", in Proc. 
         International Workshop VLBV03, September 2003. 

   [25]  van der Meer, J., Mackie, D., Swaminathan, V., Singer, D., and 
         P. Gentric, "RTP Payload Format for Transport of MPEG-4 
         Elementary Streams", RFC 3640, November 2003. 

   [26]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. 
         Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 
         3711, March 2004. 

   [27]  Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming 
         Protocol (RTSP)", RFC 2326, April 1998. 

   [28]  Handley, M., Perkins, C., and E. Whelan, "Session Announcement 
         Protocol", RFC 2974, October 2000. 

Authors' Addresses 

   Ye-Kui Wang 
   Nokia Research Center 
   P.O. Box 100 
   33721 Tampere 
   Finland 
       
   Phone: +358-50-466-7004 
   EMail: ye-kui.wang@nokia.com 
    



 
 
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   Stephan Wenger 
   Nokia 
   955 Page Mill Road 
   Palo Alto, CA 94304 
   USA 
       
   Phone: +1-650-862-7368 
   EMail: stewe@stewe.org 
    

   Miska M. Hannuksela 
   Nokia Corporation 
   P.O. Box 100 
   33721 Tampere 
   Finland 
       
   Phone: +358-40-521-2845 
   EMail: miska.hannuksela@nokia.com 
    

   Thomas Stockhammer 
   Nomor Research 
   D-83346 Bergen 
   Germany 
       
   Phone: +49-8662-419407 
   EMail: stockhammer@nomor.de 
    

   Magnus Westerlund 
   Multimedia Technologies 
   Ericsson Research EAB/TVA/A 
   Ericsson AB 
   Torshamsgatan 23 
   SE-164 80 Stockholm 
   Sweden 
       
   Phone: +46-8-7190000 
   EMail: magnus.westerlund@ericsson.com 
    







 
 
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   David Singer 
   QuickTime Engineering 
   Apple 
   1 Infinite Loop MS 302-3MT 
   Cupertino 
   CA 95014 
   USA 
       
   Phone +1 408 974-3162 
   EMail: singer@apple.com 
    

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Disclaimer of Validity 

   This document and the information contained herein are provided on an 
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   OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF 
   THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED 
   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 


 
 
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Copyright Statement 

   Copyright (C) The IETF Trust (2008). 

   This document is subject to the rights, licenses and restrictions 
   contained in BCP 78, and except as set forth therein, the authors 
   retain all their rights. 

Acknowledgement 

   Funding for the RFC Editor function is currently provided by the 
   Internet Society. 

16. Backward compatibility to RFC 3984 

   The current document is a revision of RFC 3984 and intends to 
   obsolete it.  This section addresses the backward compatibility 
   issues. 

   TBD. 

17. Changes from RFC 3984 

17.1. Technical changes 

   The technical changes (including bug fixes) from RFC 3984 are: 

   1) In subsections 5.4, 5.5, 6.2, 6,3 and 6.4, removed that the 
     packetization mode in use may be signaled by external means.  

   2) In subsection 7.2.2, changed the sentence  

      There are N VCL NAL units in the deinterleaving buffer. 

      to 

      There are N or more VCL NAL units in the deinterleaving buffer. 

   3) In subsection 7.2.2, changed the sentence  

      Herein, n corresponds to the NAL unit having the greatest value 
      of AbsDON among the received NAL units. 

      to 

      Herein, n corresponds to the NAL unit having the greatest value 
      of AbsDON among the NAL units in the deinterleaving buffer. 
 
 
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   4) In subsection 8.1, the semantics of sprop-init-buf-time, paragraph 
     2, changed the sentence 

      The parameter is the maximum value of (transmission time of a NAL 
      unit - decoding time of the NAL unit), assuming reliable and 
      instantaneous transmission, the same timeline for transmission 
      and decoding, and that decoding starts when the first packet 
      arrives. 

      to 

      The parameter is the maximum value of (decoding time of the NAL 
      unit - transmission time of a NAL unit), assuming reliable and 
      instantaneous transmission, the same timeline for transmission 
      and decoding, and that decoding starts when the first packet 
      arrives. 

   5) In subsection 8.1, removed the specification of parameter-add. 
     Other descriptions of parameter-add (in subsections 8.2 and 8.4) 
     are also removed.  

   6) In subsection 8.1, added the specification text of spatial-
     resolution, and the use of this parameter is added to subsections 
     8.2 and 8.3.  

   7) In subsection 8.2.2, changed bullet item 1, such that in the SDP 
     offer/answer model, the use of the level part of "profile-level-
     id" does not need to be symmetric, i.e. the value of the level 
     part in the answer does not have not be the same as in the offer. 
     In addition, an informative note was added to clarify the 
     specification of level 1b in H.264. 

   8) In subsection 8.2.2, changed bullet item 3 from 

      The capability parameters ("max-mbps", "max-fs", "max-cpb", "max-
      dpb", "max-br", ,"redundant-pic-cap", "max-rcmd-nalu-size") MAY 
      be used to declare further capabilities.  Their interpretation 
      depends on the direction attribute.  When the direction attribute 
      is sendonly, then the parameters describe the limits of the RTP 
      packets and the NAL unit stream that the sender is capable of 
      producing.  When the direction attribute is sendrecv or recvonly, 
      then the parameters describe the limitations of what the receiver 
      accepts. 

      to 


 
 
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      The capability parameters ("max-mbps", "max-fs", "max-cpb", "max-
      dpb", "max-br", ,"redundant-pic-cap", "max-rcmd-nalu-size") MAY 
      be used to declare further capabilities.  These parameters can 
      only be present when the direction attribute is sendrecv or 
      recvonly, and the parameters describe the limitations of what the 
      receiver accepts. 

      Such that the description matches the semantics of these 
      parameters defined earlier.  

   9) In subsection 8.2.2. the following paragraph  

      For streams being delivered over multicast, the following rules 
      apply in addition: 

      was changed to the following (with an item added after the 
      paragraph):  

      For streams being delivered over multicast, the following rules 
      apply: 

       o The media format configuration is identified by the same 
          parameters as above for unicast (i.e. "profile-level-id", 
          "packetization-mode", and, if required by "packetization-
          mode", "sprop-deint-buf-req").  These media format 
          configuration parameters (including the level part of 
          "profile-level-id") MUST be used symmetrically; i.e., the 
          answerer MUST either maintain all configuration parameters or 
          remove the media format (payload type) completely.  

      Because some items described above for unicast do not apply for 
      multicast.  

   10)In subsection 8.2.2, the bullet item starting with "In an offer or 
     answer for which the direction attribute "a=sendonly" is included 
     for the media stream, the following interpretation of the 
     parameters MUST be used:", removed the following, because, the 
     direction attribute is sendonly, the sender will not receive 
     streams. 

      Declaring the capabilities of the sender when it receives a 
      stream: 

         - max-mbps 
         - max-fs 
         - max-cpb 
         - max-dpb 
 
 
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         - max-br 
         - redundant-pic-cap 
         - deint-buf-cap 
         - max-rcmd-nalu-size 

17.2. Editorial changes 

   The editorial changes from RFC 3984 are: 

   1) In subsection 4.1 (Definitions), added the definition of "NALU-
     time" (moved from subsection 5.7 with slight modifications), and 
     changed the use of "NALU time" to "NALU-time" at two places in 
     subsection 5.7. 

   2) Added the subsection number 4.2 for Abbreviations. 

   3) In subsection 5.2, added the following paragraph right before 
     Table 1: 

      Table 1 summarizes NAL unit types and the corresponding RTP 
      packet types when each of these NAL units is directly used a 
      packet payload, and where the types are described in this memo.  

   4) In subsection 5.2, changed Table 1 from  

     Table 1.  Summary of NAL unit types and their payload structures 

      Type   Packet    Type name                        Section 
      --------------------------------------------------------- 
      0      undefined                                    - 
      1-23   NAL unit  Single NAL unit packet per H.264   5.6 
      24     STAP-A    Single-time aggregation packet     5.7.1 
      25     STAP-B    Single-time aggregation packet     5.7.1 
      26     MTAP16    Multi-time aggregation packet      5.7.2 
      27     MTAP24    Multi-time aggregation packet      5.7.2 
      28     FU-A      Fragmentation unit                 5.8 
      29     FU-B      Fragmentation unit                 5.8 
      30-31  undefined                                    - 
    
      to 

     Table 1.  Summary of NAL unit types and the corresponding packet 
                                   types  




 
 
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      NAL Unit  Packet    Packet Type Name               Section 
      Type      Type 
      --------------------------------------------------------- 
      0        undefined                                    - 
      1-23     NAL unit  Single NAL unit packet             5.6 
      24       STAP-A    Single-time aggregation packet     5.7.1 
      25       STAP-B    Single-time aggregation packet     5.7.1 
      26       MTAP16    Multi-time aggregation packet      5.7.2 
      27       MTAP24    Multi-time aggregation packet      5.7.2 
      28       FU-A      Fragmentation unit                 5.8 
      29       FU-B      Fragmentation unit                 5.8 
      30-31    undefined                                    - 
    
   5) In subsection 5.3, removed "greater than 00" from the following 
     sentence: 

      In addition to the specification above, according to this RTP 
      payload specification, values of NRI indicate the relative 
      transport priority, as determined by the encoder. 

   6) In subsection 5.3, the second informative note, corrected "nal 
     unit" to "NAL unit". 

   7) In the end of subsection 5.4, changed the text starting from the 
     second sentence of the last text paragraph and Table 3 from  

      The used packetization mode governs which NAL unit types are 
      allowed in RTP payloads.  Table 3 summarizes the allowed NAL unit 
      types for each packetization mode.  Some NAL unit type values 
      (indicated as undefined in Table 3) are reserved for future 
      extensions.  NAL units of those types SHOULD NOT be sent by a 
      sender and MUST be ignored by a receiver.  For example, the Types 
      1-23, with the associated packet type "NAL unit", are allowed in 
      "Single NAL Unit Mode" and in "Non-Interleaved Mode", but 
      disallowed in "Interleaved Mode".  Packetization modes are 
      explained in more detail in section 6. 

    Table 3.  Summary of allowed NAL unit types for each packetization 
            mode (yes = allowed, no = disallowed, ig = ignore) 








 
 
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      Type   Packet    Single NAL    Non-Interleaved    Interleaved 
                       Unit Mode           Mode             Mode 
      ------------------------------------------------------------- 
      0      undefined     ig               ig               ig 
      1-23   NAL unit     yes              yes               no 
      24     STAP-A        no              yes               no 
      25     STAP-B        no               no              yes 
      26     MTAP16        no               no              yes 
      27     MTAP24        no               no              yes 
      28     FU-A          no              yes              yes 
      29     FU-B          no               no              yes 
      30-31  undefined     ig               ig               ig 
    
      to  

      The used packetization mode governs which NAL unit types are 
      allowed in RTP payloads.  Table 3 summarizes the allowed packet 
      payload types for each packetization mode.  Packetization modes 
      are explained in more detail in section 6. 

    Table 3.  Summary of allowed NAL unit types for each packetization 
            mode (yes = allowed, no = disallowed, ig = ignore) 

      Payload Packet    Single NAL    Non-Interleaved    Interleaved 
      Type    Type      Unit Mode           Mode             Mode 
      ------------------------------------------------------------- 
      0      undefined     ig               ig               ig 
      1-23   NAL unit     yes              yes               no 
      24     STAP-A        no              yes               no 
      25     STAP-B        no               no              yes 
      26     MTAP16        no               no              yes 
      27     MTAP24        no               no              yes 
      28     FU-A          no              yes              yes 
      29     FU-B          no               no              yes 
      30-31  undefined     ig               ig               ig 
 
      Some NAL unit or payload type values (indicated as undefined in 
      Table 3) are reserved for future extensions.  NAL units of those 
      types SHOULD NOT be sent by a sender (direct as packet payloads, 
      or as aggregation units in aggregation packets, or as fragmented 
      units in FU packets) and MUST be ignored by a receiver.  For 
      example, the payload types 1-23, with the associated packet type 
      "NAL unit", are allowed in "Single NAL Unit Mode" and in "Non-
      Interleaved Mode", but disallowed in "Interleaved Mode".  
      However, NAL units of NAL unit types 1-23 can be used in 
      "Interleaved Mode" as aggregation units in STAP-B, MTAP16 and 
      MTAP14 packets as well as fragmented units in FU-A and FU-B 
 
 
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      packets.  Similarly, NAL units of NAL unit types 1-23 can also be 
      used in the "Non-Interleaved Mode" as aggregation units in STAP-A 
      packets or fragmented units in FU-A packets, in addition to being 
      directly used as packet payloads.   

   8) In subsections 5.6 and 5.7, changed "type" to "Type" in Figures 2 
     and 3. 

   9) Corrected the titles of Figures 7,8,12, and 13, wherein "and" was 
     replaced by "containing". 

   10)In subsection 5.7.2, corrected the sentence  

      The DON of the following NAL unit is equal to (DONB + DOND) % 
      65536, in which % denotes the modulo operation. 

      to 

      The DON of the NAL unit contained in a multi-time aggregation 
      unit is equal to (DONB + DOND) % 65536, in which % denotes the 
      modulo operation. 

   11)In Figure 11, corrected "NALU unit size" to "NAL unit size". 

   12)In subsection 5.7.2, the informative note under Figure 11, 
     corrected the first sentence from  

      The "earliest" multi-time aggregation unit is the one that would 
      have the smallest extended RTP timestamp among all the 
      aggregation units of an MTAP if the aggregation units were 
      encapsulated in single NAL unit packets. 

      to 

      The "earliest" multi-time aggregation unit is the one that would 
      have the smallest extended RTP timestamp among all the 
      aggregation units of an MTAP if the NAL units contained in the 
      aggregation units were encapsulated in single NAL unit packets. 

   13)In subsection 5.7.3, corrected the following sentence by replacing 
     "picture" with "NAL unit". 

      The fragmentation mechanism allows fragmenting a single picture 
      and applying generic forward error correction as described in 
      section 12.5. 


 
 
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   14)In subsection 5.7.3, changed the following sentence by replacing 
     'A' with "An". 

      A FU payload MAY have any number of octets and MAY be empty. 

   15)In subsection 5.7.3, the last informative note, changed the last 
     sentence from  

      However, the (potential) use of zero-length NALUs should be 
      carefully weighed against the increased risk of the loss of the 
      NALU because of the additional packets employed for its 
      transmission. 

      to 

      However, the (potential) use of zero-length NALU fragments should 
      be carefully weighed against the increased risk of the loss of at 
      least a part of the NALU because of the additional packets 
      employed for its transmission. 

   16)In subsection 6.1, corrected the sentence 

      Coded slice NAL units or coded slice data partition NAL units 
      belonging to the same coded picture (and thus sharing the same 
      RTP timestamp value) MAY be sent in any order permitted by the 
      applicable profile defined in [1]; however, for delay-critical 
      systems, they SHOULD be sent in their original coding order to 
      minimize the delay.  Note that the coding order is not 
      necessarily the scan order, but the order the NAL packets become 
      available to the RTP stack. 

      to 

      Coded slice NAL units or coded slice data partition NAL units 
      belonging to the same coded picture (and thus sharing the same 
      RTP timestamp value) MAY be sent in any order; however, for 
      delay-critical systems, they SHOULD be sent in their original 
      decoding order to minimize the delay.  Note that the decoding 
      order is the order of the NAL units in the bitstream. 

   17)Removed "(Informative)" from the tile of section 7, and changed 
     the first sentences in the beginning of section 7 from 

      The de-packetization process is implementation dependent.  
      Therefore, the following description should be seen as an example 
      of a suitable implementation.  Other schemes may be used as well.  

 
 
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      Optimizations relative to the described algorithms are likely 
      possible.   

      to  

      The de-packetization process is implementation dependent.  
      Therefore, the following description should be seen as an example 
      of a suitable implementation.  Other schemes may be used as well 
      as long as the output for the same input is the same as the 
      process described below.  The output is the same meaning that the 
      number of NAL units and their order are both the identical.  
      Optimizations relative to the described algorithms are likely 
      possible.   

   18)In subsection 7.1, paragraph 1, corrected the last sentence from  

      If a decapsulated packet is an FU-A, all the fragments of the 
      fragmented NAL unit are concatenated and passed to the decoder. 

      to 

      For all the FU-A packets containing fragments of a single NAL 
      unit, the decapsulated fragments are concatenated in their 
      sending order to recover the NAL unit, which is then passed to 
      the decoder. 

   19)In subsection 7.2, paragraph 2, corrected the first sentence 
     (copied below) by replacing "packets" with "NAL units". 

      The receiver includes a receiver buffer, which is used to 
      compensate for transmission delay jitter and to reorder packets 
      from transmission order to the NAL unit decoding order. 

   20)In subsection 7.2.2, paragraph 1, changed the following sentence 
     by replacing "is" with "are". 

      After initial buffering, decoding and playback is started, and 
      the buffering-while-playing mode is used. 

   21)In subsection 7.2.2, paragraph 1, changed the sentence 

      The value of DON is calculated and stored for all NAL units. 

      to 

      The value of DON is calculated and stored for each NAL unit. 

 
 
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   22)In subsection 7.2.2, removed "an" from the following sentence. 

      Let PDON be a variable that is initialized to 0 at the beginning 
      of the an RTP session. 

   23)In section 8, paragraph 2, changed the sentence  

      The name of all these parameters starts with "sprop" for stream 
      properties. 

      to 

      The names of all these parameters start with "sprop" for stream 
      properties. 

   24)In subsection 8.1, the semantics of max-mbps, max-fs, max-cpb, 
     max-dpb, and max-br, changed the last paragraph above the 
     informative note from  

         A receiver MUST NOT signal values of max-mbps, max-fs, max-
         cpb, max-dpb, and max-br that meet the requirements of a 
         higher level, referred to as level A herein, compared to the 
         level specified in the value of the profile-level-id 
         parameter, if the receiver can support all the properties of 
         level A. 

      to  

         If a receiver can support all the properties of level A, the 
         level specified in the value of the profile-level-id MUST be 
         level A (i.e. MUST NOT be lower than level A).  In other 
         words, a sender or receiver MUST NOT signal values of max-
         mbps, max-fs, max-cpb, max-dpb, and max-br that meet the 
         requirements of a higher level compared to the level specified 
         in the value of the profile-level-id parameter.  

   25)In subsection 8.1, the semantics of max-dpb, the informative note, 
     removed "and is a property of the video decoder only" from the 
     following sentence. 

      The decoded picture buffer stores reconstructed samples and is a 
      property of the video decoder only. 

   26)In subsection 8.1, the semantics of max-br, paragraph 2, removed 
     the following sentence that is repeated later in the exact form. 


 
 
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      The value of max-br MUST be greater than or equal to the value of 
      MaxBR for the level given in Table A-1 of [1]. 

   27)In subsection 8.1, the semantics of packetization-mode, changed 
     the last sentence from  

      The value of packetization mode MUST be an integer in the range 
      of 0 to 2, inclusive. 

      to  

      The value of packetization-mode MUST be an integer in the range 
      of 0 to 2, inclusive. 

   28)In subsection 8.1, the semantics of sprop-init-buf-time, paragraph 
     2, changed the following sentence by replacing "MUST buffer" by 
     "MUST wait". 

      The parameter signals the initial buffering time that a receiver 
      MUST buffer before starting decoding to recover the NAL unit 
      decoding order from the transmission order. 

   29)In subsection 8.1, changed "NAL unit stream" to "RTP packet 
     stream" at several places in the semantics of sprop-interleaving-
     depth, sprop-deint-buf-req, sprop-init-buf-time and sprop-max-don-
     diff.  

   30)In subsection 8.1, removed the paragraph talking about file 
     formats after the description of "Encoding considerations".  The 
     references 29 and 30 (to file format specifications) were also 
     removed.  

   31)In subsection 8.2.1, the example SDP message. Added the required 
     parameter "packetization-mode", which was missing. The use of 
     spatial-resolution is also added.  The third change is the change 
     of a hypothetical value of "sprop-parameter-sets" to "<base64 
     data>", as readers may be confused by the hypothetical value.  The 
     same change regarding hypothetical values of "sprop-parameter-
     sets" was made to the SDP examples in subsection 8.3.  

   32)In subsection 8.2.2, bullet item 2, changed the beginning sentence 
     from  

      The parameters "sprop-parameter-sets", "sprop-deint-buf-req", 
      "sprop-interleaving-depth", "sprop-max-don-diff", and "sprop-
      init-buf-time" describe the properties of the NAL unit stream 

 
 
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      that the offerer or answerer is sending for this media format 
      configuration. 

      to  

      The parameters "packetization-mode", and if present, "sprop-
      deint-buf-req", "sprop-parameter-sets", "sprop-interleaving-
      depth", "sprop-max-don-diff", and "sprop-init-buf-time", describe 
      the properties of the RTP packet stream that the offerer or 
      answerer is sending for this media format configuration.   

   33)In subsection 8.2.2, bullet item 2, the informative note, the last 
     sentence, corrected the typo "then" to "than". 

   34)In subsection 8.2.2, changed the following bullet item for 
     multicast  

        o The stream properties parameters ("sprop-parameter-sets", 
          "sprop-deint-buf-req", "sprop-interleaving-depth", "sprop-
          max-don-diff", and "sprop-init-buf-time") MUST NOT be changed 
          by the answerer.  Thus, a payload type can either be accepted 
          unaltered or removed. 

      to  

        o The stream properties parameters ("sprop-parameter-sets", 
          "sprop-interleaving-depth", "sprop-max-don-diff", and "sprop-
          init-buf-time") MUST NOT be changed by the answerer.  Thus, a 
          payload type can either be accepted unaltered or removed. 

   35)In subsection 8.2.3, changed two uses of "NAL unit stream" to "RTP 
     packet stream", and changed the sentence "Declaring actual 
     configuration or properties:" to "Declaring actual configuration 
     or stream properties:". 

   36)In subsection 8.3, the first sentence, changed "A SIP Offer/Answer 
     exchange" to "An SDP Offer/Answer exchange". 

   37)In subsection 8.3, the first example, changed "Offerer -> Answer 
     SDP message:" to "Offerer -> Answerer SDP message:". 

   38)In subsection 8.3, in the paragraph describing the offer SDP in 
     the first example, changed  

      PT 98 represents single NALU mode, PT 99 non-interleaved mode; PT 
      100 indicates the interleaved mode.   

 
 
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      to  

      PT 98 represents single NALU mode, PT 99 represents non-
      interleaved mode, and PT 100 indicates the interleaved mode.   

      And changed "that are required for the answerer" to "that are 
      required by the answerer". 

      And changed  

      Note that the value for "sprop-parameter-sets", although 
      identical in the example above, could be different for each 
      payload type. 

      to 

      Note that the value for "sprop-parameter-sets" could be different 
      for each payload type. 

   39)In subsection 8.3, changed the two paragraphs describing the 
     answer SDP in the first example from 

      As the Offer/Answer negotiation covers both sending and receiving 
      streams, an offer indicates the exact parameters for what the 
      offerer is willing to receive, whereas the answer indicates the 
      same for what the answerer accepts to receive.  In this case the 
      offerer declared that it is willing to receive payload type 98.  
      The answerer accepts this by declaring a equivalent payload type 
      97; i.e., it has identical values for the three parameters 
      "profile-level-id", packetization-mode, and "sprop-deint-buf-
      req".  This has the following implications for both the offerer 
      and the answerer concerning the parameters that declare 
      properties.  The offerer initially declared a certain value of 
      the "sprop-parameter-sets" in the payload definition for PT=98.  
      However, as the answerer accepted this as PT=97, the values of 
      "sprop-parameter-sets" in PT=98 must now be used instead when the 
      offerer sends PT=97.  Similarly, when the answerer sends PT=98 to 
      the offerer, it has to use the properties parameters it declared 
      in PT=97. 

      The answerer also accepts the reception of the two configurations 
      that payload types 99 and 100 represent.  It provides the initial 
      parameter sets for the answerer-to-offerer direction, and for 
      buffering related parameters that it will use to send the payload 
      types.  It also provides the offerer with its memory limit for 
      deinterleaving operations by providing a "deint-buf-cap" 
      parameter.  This is only useful if the offerer decides on making 
 
 
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      a second offer, where it can take the new value into account.  
      The "max-rcmd-nalu-size" indicates that the answerer can 
      efficiently process NALUs up to the size of 3980 bytes.  However, 
      there is no guarantee that the network supports this size. 

      to 

      As the Offer/Answer negotiation covers both sending and receiving 
      streams, an offer indicates the exact parameters for what the 
      offerer is willing to receive, whereas the answer indicates the 
      same for what the answerer accepts to receive.  In this case the 
      offerer declared that it is willing to receive payload type 98.  
      The answerer accepts this by declaring an equivalent payload type 
      97; i.e., it has identical values for the two parameters 
      "profile-level-id" and "packetization-mode" (since 
      "packetization-mode" is equal to 0, "sprop-deint-buf-req" is not 
      present).  As the offered payload type 98 is accepted, the 
      answerer needs to store parameter sets included in sprop-
      parameter-sets=<base64 data#0> in case the offer finally decides 
      to use this configuration. In the answer, the answerer includes 
      the parameter sets in sprop-parameter-sets=<base64 data#3> that 
      the answerer would use in the stream sent from the answerer if 
      this configuration is finally used.  

      The answerer also accepts the reception of the two configurations 
      that payload types 99 and 100 represent.  Again, the answerer 
      needs to store parameter sets included in sprop-parameter-
      sets=<base64 data#1> and sprop-parameter-sets=<base64 data#2> in 
      case the offer finally decides to use either of these two 
      configurations.  The answerer provides the initial parameter sets 
      for the answerer-to-offerer direction, i.e. the parameter sets in 
      sprop-parameter-sets=<base64 data#4> and sprop-parameter-
      sets=<base64 data#5>, for payload types 99 and 100, respectively, 
      that it will use to send the payload types.  The answerer also 
      provides the offerer with its memory limit for deinterleaving 
      operations by providing a "deint-buf-cap" parameter.  This is 
      only useful if the offerer decides on making a second offer, 
      where it can take the new value into account.  The "max-rcmd-
      nalu-size" indicates that the answerer can efficiently process 
      NALUs up to the size of 3980 bytes.  However, there is no 
      guarantee that the network supports this size. 

   40)In the end of subsection 8.3, added four more SDP offer/answer 
     examples describing level downgrade and using or not using out-of-
     band transmission of parameter sets.  


 
 
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   41)In subsection 8.4, changed two uses of "RTP stream" to "RTP packet 
     stream".  

   42)In subsection 8.4, changed the sentence  

      It is RECOMMENDED that parameter set IDs be partitioned between 
      the out-of-band and in-band parameter sets. 

      to 

      It is therefore RECOMMENDED that parameter set IDs be partitioned 
      between the out-of-band and in-band parameter sets. 

   43)In subsection 13.3, changed 

      pictures are transmitted at constant intervals (that is, 1 / 
      frame rate). 

      to 

      pictures are transmitted at constant intervals (that is, 1 / 
      (frame rate)). 

18. Open issues 

   The issues remaining open are: 

   1) Rules of SDP usage for spatial-resolution need to be further 
     specified, e.g., what if a resolution requested by a receiver is 
     not supported by the sender even the resolution is within the 
     agreed level limit? 

   2) In subsection 8.2, the following sentence, what are the "non-
     downgradable parameters"? It was defined earlier that a 
     configuration consists of three parameters, "profile-level-id", 
     "packetization-mode", and, if required by "packetization-mode", 
     "sprop-deint-buf-req". Isn't it confusing to say that other 
     parameters "express a configuration"? What does "acceptable" mean, 
     acceptable to the sender for receiving a stream using the 
     configuration? 

      When a sender's capabilities are declared, and non-downgradable 
      parameters are used in this declaration, then these parameters 
      express a configuration that is acceptable.  

   3) A question related to the first SDP usage example in subsection 
     8.2.3: If the answer accepts more than one alternative in the 
 
 
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     offer, and the offer/answer stops, is it so that the offerer can 
     now freely choose one of the alternatives accepted by the 
     answerer? 

   4) Subsection 8.2.3, in the following explanatory text for the first 
     SDP usage example, what does the second sentence mean? If the 
     offer stops offer/answer, should the offer take into account the 
     value of the parameter when sending a stream? If yes, then the 
     sentence should be removed or reworded. 

      The answerer also provides the offerer with its memory limit for 
      deinterleaving operations by providing a "deint-buf-cap" 
      parameter.  This is only useful if the offerer decides on making 
      a second offer, where it can take the new value into account.  T 

   5) Integration of draft-ietf-avt-rtp-h264-params-01.txt remains to be 
     done. 

   6) To complete the section on backward compatibility to RFC 3984. 

 

 

 

    




















 
 
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