Network Working Group S. Wenger Internet-Draft Y.-K. Wang Intended status: Standards Track Nokia Expires: June 17, 2008 T. Schierl Fraunhofer HHI December 18, 2007 RTP Payload Format for SVC Video draft-ietf-avt-rtp-svc-04.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 Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on June 17, 2008. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This memo describes an RTP payload format for scalable video coding (SVC) defined in Annex G of the ITU-T Recommendation H.264 video codec which is technically identical to Amendment 3 of ISO/IEC International Standard 14496-10. The RTP payload format allows for packetization of one or more Network Abstraction Layer (NAL) units, produced by the video encoder, in each RTP packet payload. The payload format has wide applicability, such as low bit-rate conversational, Internet video streaming, or high bit-rate entertainment quality video. Wenger, Wang, Schierl Expires June 17, 2008 [Page 1] Internet-Draft RTP Payload Format for SVC Video December 2007 Table of Contents RTP Payload Format for SVC Video...................................... 1 1. Introduction ................................................. 4 2. Conventions .................................................. 4 3. The SVC Codec ................................................ 4 3.1. Overview ..................................................... 4 3.2. Parameter Set Concept ........................................ 6 3.3. Network Abstraction Layer Unit Header ........................ 6 4. Scope ........................................................ 9 5. Definitions and Abbreviations ................................ 9 5.1. Definitions .................................................. 9 5.1.1. Definitions per SVC specification ............................ 9 5.1.2. Definitions local to this memo .............................. 11 5.2. Abbreviations ............................................... 12 6. RTP Payload Format .......................................... 12 6.1. Design Principles ........................................... 12 6.2. RTP Header Usage ............................................ 13 6.3. Common Structure of the RTP Payload Format .................. 13 6.4. NAL Unit Header Usage ....................................... 13 6.5. Packetization Modes ......................................... 14 6.6. Decoding Order Number (DON) ................................. 14 6.7. Aggregation Packets ......................................... 15 6.8. Fragmentation Units (FUs) ................................... 15 6.9. Payload Content Scalability Information (PACSI) NAL Unit .... 15 7. Packetization Rules ......................................... 20 8. De-Packetization Process (Informative) ...................... 21 8.1. De-Packetization Process for NAL Units Conveyed using Session Multiplexing......................................................... 22 8.1.1. De-Packetization Process for Session Multiplexing using non- interleaved mode or Single NAL unit mode without the use of CL-DON... 22 8.1.2. De-Packetization Process for Session Multiplexing using CL-DON 25 9. Payload Format Parameters ................................... 26 9.1. Media Type Registration ..................................... 27 9.2. SDP Parameters .............................................. 43 9.2.1. Mapping of Payload Type Parameters to SDP ................... 44 9.2.2. Usage with the SDP Offer/Answer Model ....................... 44 9.2.3. Usage with Session Multiplexing ............................. 48 9.2.4. Usage in Declarative Session Descriptions ................... 49 9.3. Examples .................................................... 49 9.3.1. Example for offering a single SVC session ................... 49 9.3.2. Example for offering session multiplexing ................... 50 9.4. Parameter Set Considerations ................................ 50 10. Security Considerations ..................................... 50 11. Congestion Control .......................................... 51 12. IANA Consideration .......................................... 51 13. Informative Appendix: Application Examples .................. 52 13.1. Introduction ................................................ 52 13.2. Layered Multicast ........................................... 52 Wenger, Wang, Schierl Expires June 17, 2008 [Page 2] Internet-Draft RTP Payload Format for SVC Video December 2007 13.3. Streaming of an SVC scalable stream ......................... 53 13.4. Multicast to MANE, SVC scalable stream to endpoint .......... 53 13.5. Scenarios currently not considered for being unaligned with IP philosophy........................................................... 55 13.6. SSRC Multiplexing ........................................... 56 14. References .................................................. 56 14.1. Normative References ........................................ 56 14.2. Informative References ...................................... 57 15. Author's Addresses .......................................... 57 16. Copyright Statement ......................................... 58 17. Disclaimer of Validity ...................................... 58 18. Intellectual Property Statement ............................. 58 19. Acknowledgement ............................................. 59 20. RFC Editor Considerations ................................... 59 21. Open Issues ................................................. 59 22. Changes Log ................................................. 59 Wenger, Wang, Schierl Expires June 17, 2008 [Page 3] Internet-Draft RTP Payload Format for SVC Video December 2007 1. Introduction This memo specifies an RTP [RFC3550] payload format for the Scalable Video Coding (SVC) extension of the H.264/AVC video coding standard. Formally, SVC takes the form of Amendment 3 to ISO/IEC 14496 Part 10 [MPEG4-10], and Annex G of ITU-T Rec. H.264 [H.264]. The specification of SVC is available in [SVC]. SVC covers the whole application ranges of H.264/AVC, starting with low bit-rate Internet streaming applications to HDTV broadcast and Digital Cinema with nearly lossless coding and requiring dozens or hundreds of MBit/s. This memo tries to follow a backward compatible enhancement philosophy similar to what the video coding standardization committees implement, by keeping as close an alignment to the H.264/AVC payload format [RFC3984] as possible. It documents the enhancements relevant from an RTP transport viewpoint, and defines signaling support for SVC, including a new media subtype name. This memo includes two processes for recovery of NAL unit decoding order of NAL units transported using multiple RTP sessions, when using of the interleaved mode is not required. The first uses the cross-layer decoding order number, as specified in 8.1.2. The second uses timestamp etc., as specified in 8.1.1. The first process has been agreed by the editors, but having the second process in addition has not been agreed by the editors. The editors therefore request the AVT to make a decision whether to have the second process in addition. 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 BCP 14, RFC 2119 [RFC2119]. 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. The SVC Codec 3.1. Overview SVC provides scalable video bitstreams. In SVC, a scalable video bitstream contains a base layer conforming to at least one of the profiles of H.264/AVC as defined in Annex A of [H.264], and one or more enhancement layers, collectively denoted as Layers. A Layer may be the base Layer or enhance the temporal resolution (i.e. the frame rate), the spatial resolution, or the quality of the video content, relative Wenger, Wang, Schierl Expires June 17, 2008 [Page 4] Internet-Draft RTP Payload Format for SVC Video December 2007 to the quality represented without the Layer. Note, that the definition of Layer in this memo encompasses temporal, spatial and fidelity enhancements. Each RTP session can carry NAL units belonging to one or more Layers. The NAL unit headers include information associating a given NAL unit to a Layer. Therefore, extracting individual Layers from an RTP session containing more than one Layer is a lightweight operation, involving only fixed length bit fields in the header, as documented in this memo and in [SVC]. Multiple RTP sessions, regardless of whether each carries a single Layer or multiple Layers as discussed above, can be used to transport the whole scalable bitstream, or Operation Points thereof. An Operation Point consists of only those Layers necessary to reconstruct a given quality (in temporal, spatial and fidelity dimensions). The concept of video coding layer (VCL) and network abstraction layer (NAL) is inherited from H.264/AVC. The VCL contains the signal processing functionality of the codec; mechanisms such as transform, quantization, motion-compensated prediction, loop filtering and inter- layer prediction. A coded picture in H.264/AVC consists of one or more slices. Within one access unit, a coded picture of an Operation Point consists of all the coded slices required for decoding up to a particular Layer at the time instance corresponding to the access unit. The Network Abstraction Layer (NAL) encapsulates each slice generated by the VCL into one or more Network Abstraction Layer Units (NAL units). Please consult RFC 3984 for a more in-depth discussion of the NAL unit concept. SVC specifies the decoding order of NAL units. "Layer" in the terms "Video Coding Layer" and "Network Abstraction Layer" refers to a conceptual distinction, and is closely related to syntax layers (block, macroblock, slice, ... layers). "Layer" here describes a syntax level of the bitstream in contrast to a part of the layered bitstream, which may be discarded. It should not be confused with base and enhancement Layers. The concept of temporal scalability is not newly introduced by SVC, as profiles defined in Annex A of [H.264] already support it. In [H.264], sub-sequences have been introduced in order to allow optional use of temporal layers. SVC extends this approach by advertising the temporal scalability information within the NAL unit header, or prefix NAL units, as discussed in section 3.3 of this memo and in [SVC]. The concept of scaling the visual content quality in the granularity of complete enhancement Layers, i.e. through omitting the transport and decoding of entire Layers, is denoted as spatial scalability or Signal- to-Noise Ratio (SNR) scalability, the latter is also know as Coarse- Grained Scalability (CGS). This is what is commonly understood as scalability in the IETF community. In addition, SVC also offers the concept of another type of SNR scalability, the Medium-Grained Scalability (MGS). MGS involves selectively omitting the decoding of Wenger, Wang, Schierl Expires June 17, 2008 [Page 5] Internet-Draft RTP Payload Format for SVC Video December 2007 NAL units belonging to MGS layers. The selection of the NAL units to omit can be based on fixed length fields in the NAL unit header. 3.2. Parameter Set Concept The parameter set concept is inherited from [H.264]. Please refer to section 1.2 of RFC 3984 for more details. SVC introduced a new type of sequence parameter set, referred to as subset sequence parameter set. Subset sequence parameter sets have NAL unit type equal to 15, which is different from the NAL unit type value (7) of sequence parameter set. VCL NAL units of NAL unit type 1 to 5 must only (indirectly) refer to sequence parameter sets, while VCL NAL units of NAL unit type 20 must only (indirectly) refer to subset sequence parameter sets. Subset sequence parameter sets use a separate identifier value space than sequence parameter sets. In SVC, pictures from different Layers, defined as layer representations in [SVC] (Note: A layer representation in [SVC] is identified by a single combination of dependency_id and quality_id values), may use the same sequence or picture parameter set, but may also use different sequence or picture parameter sets. If different sequence parameter sets are used, then, at any time instant during the decoding process, there may be one active sequence parameter set (for the layer representation with the highest value of (dependency_id * 16 + quality_id)) and one or more active layer sequence parameter set(s) (for layer representations with lower values of (dependency_id * 16 + quality_id)). Any specific active sequence parameter set or active layer sequence parameter set remains unchanged throughout a coded video sequence in the Layer in which the active sequence parameter set or active layer sequence parameter set is referred to. This means that the referred sequence parameter set or subset sequence parameter set can only change at IDR access units for any Layer. [Ed. May need to have a "layer" definition to be used here, such as "dependency layer" identified by dependency_id, or "quality layer", identified by quality_id. One issue with the current Layer definition is that, a Layer of temporal_id greater than 0 would not contain an IDR access unit. And the SPS application scope includes all temporal Layers.] The active picture parameter set remains unchanged within a layer representation. 3.3. Network Abstraction Layer Unit Header An SVC NAL unit consists of a header of four octets and the payload byte string. SVC NAL units of type 20 encapsulate VCL data as defined in Annex G of [SVC]. A special type of an SVC NAL unit is the prefix NAL unit (type 14) that includes descriptive information of the associated H.264/AVC VCL NAL unit (type 1 or 5) that immediately follows the prefix NAL unit. SVC extends the one-byte H.264/AVC NAL unit header by three additional octets. The header indicates the type of the NAL unit, the (potential) Wenger, Wang, Schierl Expires June 17, 2008 [Page 6] Internet-Draft RTP Payload Format for SVC Video December 2007 presence of bit errors or syntax violations in the NAL unit payload, information regarding the relative importance of the NAL unit for the decoding process, the layer identification information, and other fields as discussed below. This RTP payload specification is designed to be unaware of the octet string in the NAL unit payload. The NAL unit header 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 header are formally specified in [SVC], but the essential properties of the NAL unit header are summarized below. The first byte of the NAL unit header has the following format (the bit fields are the same as defined for the one-byte H.264/AVC NAL unit header, while the semantics of some fields have changed slightly, in a backward compatible way): +---------------+ |0|1|2|3|4|5|6|7| +-+-+-+-+-+-+-+-+ |F|NRI| Type | +---------------+ F: 1 bit forbidden_zero_bit. H.264/AVC declares a value of 1 as a syntax violation. NRI: 2 bits nal_ref_idc. A value of '00' (in binary form) indicates that the content of the NAL unit is not used to reconstruct reference pictures for future prediction. Such NAL units can be discarded without risking the integrity of the reference pictures in the same Layer. A value greater than '00' indicates that the decoding of the NAL unit is required to maintain the integrity of reference pictures in the same Layer, or that the NAL unit contains parameter sets. Type: 5 bits nal_unit_type. This component specifies the NAL unit type as defined in table 7-1 of [SVC], 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 [SVC]. In H.264/AVC, NAL unit types 14, 15 and 20 are reserved for future extensions. SVC uses these three NAL unit types. NAL unit type 14 is used for prefix NAL unit, NAL unit type 15 is used for subset sequence parameter set and NAL unit type 20 is used for coded slice in scalable extension (see section 7.4.1 in [SVC]). NAL unit types 14 and 20 indicate the presence of three additional octets in the NAL unit header, as shown below. Wenger, Wang, Schierl Expires June 17, 2008 [Page 7] Internet-Draft RTP Payload Format for SVC Video December 2007 +---------------+---------------+---------------+ |0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7|0|1|2|3|4|5|6|7| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |R|I| PRID |N| DID | QID | TID |U|D|O| RR| +---------------+---------------+---------------+ R: 1 bit reserved_one_bit. Reserved bit for future extension. R MUST be equal to 1. Receivers SHOULD discard NAL units with R equal to 0. I: 1 bit idr_flag. This component specifies whether the layer representation is an instantaneous decoding refresh (IDR) layer representation (when equal to 1) or not (when equal to 0). PRID: 6 bits priority_id. This flag specifies a priority identifier for the NAL unit. A lower value of PRID indicates a higher priority. N: 1 bit no_inter_layer_pred_flag. This flag specifies, when present in a coded slice NAL unit, whether inter-layer prediction may be used for decoding the coded slice (when equal to 1) or not (when equal to 0). DID: 3 bits dependency_id. This component denotes the inter-layer coding dependency hierarchy. At any access unit, a layer representation with a less dependency_id may be used for inter-layer prediction for coding of a layer representation with a greater dependency_id, while a layer representation with a greater dependency_id shall not be used for inter-layer prediction for coding of a layer representation with a less dependency_id. QID: 4 bits quality_id. This component designates the quality level hierarchy of a MGS layer representation. At any access unit and with identical dependency_id value, a layer representation with quality_id equal to ql uses a layer representation with quality_id equal to ql-1 for inter- layer prediction. TID: 3 bits temporal_id. This component indicates the temporal layer (or frame rate) hierarchy. Informally put, a layer consisting of layer representations with a less temporal_id corresponds to a lower frame rate. A given temporal layer typically depends on the lower temporal layers (i.e. the temporal layers with less temporal_id) but never depends on any higher temporal layer. U: 1 bit use_ref_base_pic_flag. A value of 1 indicates that only reference base pictures are used during the inter prediction process. A value of 0 Wenger, Wang, Schierl Expires June 17, 2008 [Page 8] Internet-Draft RTP Payload Format for SVC Video December 2007 indicates that the reference base pictures are not used during the inter prediction process. D: 1 bit discardable_flag. A value of 1 indicates that the current NAL unit is not used for decoding NAL units with greater dependency_id than the current NAL unit in the current and all subsequent access units. Such NAL units can be discarded without risking the integrity of higher layers with greater dependency_id. discardable_flag equal to 0 indicates that the decoding of the NAL unit is required to maintain the integrity of higher layers with greater dependency_id. O: 1 bit output_flag: Affects the decoded picture output process as defined in Annex C of [SVC]. RR: 2 bits reserved_three_2bits. Reserved bits for future extension. RR MUST be equal to '11' (in binary form). Receivers SHOULD discard NAL units with RR not equal to '11'. This memo reuses the same additional NAL unit types introduced in RFC 3984, which are presented in section 6.3. In addition, this memo introduces one OPTIONAL NAL unit type, 30, as specified in section 6.9. These NAL unit types are marked as unspecified in [SVC] and intentionally reserved for use in systems specifications like this memo. Moreover, this specification extends the semantics of F, NRI, I, PRID, DID, QID, TID, U, and D as described in section 6.4. 4. Scope This payload specification can only be used to carry the "naked" NAL unit stream over RTP, and not the byte stream format according to Annex B of [SVC]. Likely, the applications of this specification will be in the IP based multimedia communications fields including conversational multimedia, video telephony or video conferencing, Internet streaming and TV over IP. This specification allows, in a given RTP session, to encapsulate NAL units belonging to o the base Layer only, detailed specification in [RFC3984], or o one or more enhancement Layers, or o the base Layer and one or more enhancement Layers 5. Definitions and Abbreviations 5.1. Definitions 5.1.1. Definitions per SVC specification Wenger, Wang, Schierl Expires June 17, 2008 [Page 9] Internet-Draft RTP Payload Format for SVC Video December 2007 This document uses the definitions of [SVC]. The following terms, defined in [SVC], are summed up for convenience: access unit: A set of NAL units pertaining to a certain temporal location. An access unit includes the coded slices of all the scalable layers at that temporal location and possibly other associated data, e.g. supplemental enhancement information (SEI) messages and parameter sets. 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 including all subsequent access units up to but not including any subsequent IDR access unit. The coded video sequence is a Layer specific concept. See below the definition of IDR access unit. IDR access unit: An access unit in which the coded picture is an IDR picture. For a certain SVC bitstream, an access unit may be an IDR access unit for a Layer A but not an IDR access unit for Layer B, subject to the maximum present value of dependency_id within the access unit, which depends on which Layer is decoded. IDR picture: A coded picture in which all slices with the maximum present value of dependency_id within the access unit are I or EI slices that causes the decoding process to mark all reference pictures as "unused for reference" immediately after decoding the IDR picture. 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. The first picture of each coded video sequence is an IDR picture. layer representation: A subset of VCL NAL units within an access unit that are associated with identical values of dependency_id and quality_id, which are provided as part of the VCL NAL unit header or by an associated prefix NAL unit. prefix NAL unit: A NAL unit with nal_unit_type equal to 14 that immediately precedes a NAL unit with nal_unit_type equal to 1, 5, or 12. The NAL unit that succeeds the prefix NAL unit is also referred to as the associated NAL unit. The prefix NAL unit contains data associated with the associated NAL unit, which are considered to be part of the associated NAL unit. reference base picture: A decoded representation of an access unit that is only used for inter prediction reference but not for output. A reference base picture is constructed only when the store_base_rep_flag as specified in the SVC specification is equal to 1. scalable bitstream: A bitstream with the property that one or more bitstream subsets that are not identical to the scalable bitstream form another bitstream that conforms to the SVC specification. Wenger, Wang, Schierl Expires June 17, 2008 [Page 10] Internet-Draft RTP Payload Format for SVC Video December 2007 5.1.2. Definitions local to this memo anchor layer representation: An anchor layer representation is such a layer representation that, if decoding of the Layer starts from the layer representation, all the following layer representations of the Layer, in output order, can be correctly decoded. An anchor layer representation is a random access point to the Layer the anchor layer representation belongs to. However, some layer representations, succeeding an anchor layer representation in decoding order but preceding the anchor layer representation in output order, may refer to earlier layer representations for inter prediction, hence may not be correctly decoded if random access is performed at the anchor layer representation. base Layer: The base Layer is typically representing the minimal spatial resolution, the minimal fidelity, and the minimal frame rate of an SVC bitstream. In other words, the base Layer consists of all the VCL NAL units with dependency_id, quality_id and temporal_id equal to 0 and the associated non-VCL NAL units. The base Layer is independently decodable without the requirement of using any other Layer of the SVC bitstream. Note that this definition is different from the definition of "base layer" in Annex G of [SVC]. cross-layer decoding order number (CL-DON): An OPTIONAL field in the payload structure, or a derived variable indicating NAL unit decoding order over all the NAL units transported in all the RTP sessions for transporting the SVC bitstream. enhancement Layer: An SVC enhancement Layer is a Layer with any of temporal_id, dependency_id, and quality_id greater than 0. full base Layer: The bitstream containing the base Layer and the temporal enhancement Layers with dependency_id and quality_id both equal to 0. The full base Layer must conform to one of the profiles defined in Annex A of [H.264]. In SVC context each slice NAL unit in the full base Layer is associated with a prefix NAL unit, which has a four bytes NAL unit header containing all the syntax elements described in section 3.3. The full base layer is equivalent to the definition of "base layer" in Annex G of [SVC]. intra layer representation: A layer representation that contains only intra coded slices hence does not refer to any earlier layer representation in decoding order in the same layer for inter prediction. However, an intra layer representation may use inter-layer prediction for its decoding. Layer: A Layer may be the base Layer or an enhancement Layer that enhances the temporal resolution (i.e. the frame rate), the spatial resolution, or the quality of the video content, relative to the quality represented without the Layer. Wenger, Wang, Schierl Expires June 17, 2008 [Page 11] Internet-Draft RTP Payload Format for SVC Video December 2007 Operation Point: An Operation Point of an SVC bitstream represents a certain level of temporal, spatial and quality scalability. An Operation Point contains only those NAL units required for a valid bitstream (conforming to at least one of the profiles defined in Annex A or Annex G of [SVC]) to represent a certain quality. The Operation Point is described by the maximum present value of dependency_id, and, within that maximum present value of dependency_id, by the maximum quality_id and temporal_id, within the bitstream subset representing the Operation Point. RTP packet stream: A sequence of RTP packets with increasing sequence numbers (except for wrap-around), identical PT and identical SSRC (Synchronization Source), carried in one RTP session. Within the scope of this memo, one RTP packet stream is utilized to transport an integer number of SVC Layers. Session multiplexing: The scalable SVC bitstream is distributed onto different RTP sessions, whereby each RTP session carries a single RTP packet stream. Each RTP session requires a separate signaling and has a separate Timestamp, Sequence Number, and SSRC space. Dependency between sessions MUST be signaled according to [I-D.ietf-mmusic- decoding-dependency] and this memo. SVC NAL unit: A NAL unit of NAL unit type 14 or 20 as specified in Annex G of [SVC]. An SVC NAL unit has a four-byte NAL unit header. 5.2. Abbreviations In addition to the abbreviations defined in [RFC3984], the following ones are defined. CGS: Coarse-Grain Scalability CL-DON: Cross-Layer Decoding Order Number MGS: Medium-Grain Scalability PACSI: Payload Content Scalability Information SVC: Scalable Video Coding 6. RTP Payload Format 6.1. Design Principles The following design principles have been observed: o Backward compatibility with [RFC3984] wherever possible. o As the SVC full base Layer is H.264/AVC compatible, the full base Layer or any subset, when transmitted in its own session, MUST be encapsulated using [RFC3984]. Requiring this has the desirable side effect that it can be used by [RFC3984] legacy devices. o MANEs are signaling aware and rely on signaling information. MANEs have state. Wenger, Wang, Schierl Expires June 17, 2008 [Page 12] Internet-Draft RTP Payload Format for SVC Video December 2007 o MANEs can aggregate multiple RTP streams, possibly from multiple RTP sessions. o MANEs can perform media-aware stream thinning. By using the payload header information identifying Layers within an RTP session, MANEs are able to remove packets from the incoming RTP packet stream. This implies rewriting the RTP headers of the outgoing packet stream and rewriting of RTCP Receiver Reports. 6.2. RTP Header Usage Please see section 5.1 of [RFC3984]. 6.3. Common Structure of the RTP Payload Format Please see section 5.2 of [RFC3984]. 6.4. NAL Unit Header Usage The structure and semantics of the NAL unit header were introduced in section 3.3. This section specifies the semantics of F, NRI, I, PRID, DID, QID, TID, U, and D according to this specification. The semantics of F specified in section 5.3 of [RFC3984] also applies herein. For NRI, for the bitstream conforming to one of the profiles defined in Annex A of [H.264] and transported using [RFC3984], the semantics specified in section 5.3 of [RFC3984] are applicable, i.e., NRI also indicates the relative importance of NAL units. In SVC context, in addition to the semantics specified in Annex G of [SVC] are applicable, NRI also indicate the relative importance of NAL units within a Layer. For I, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to protect NAL units with I equal to 1 better than NAL units with I equal to 0. MANEs MAY also utilize information of NAL units with I equal to 1 to decide when to forward more packets for an RTP packet stream. For example, when it is sensed that spatial Layer switching has happened such that the Operation Point has changed to a higher value of DID, MANEs MAY start to forward NAL units with the higher value of DID only after forwarding a NAL unit with I equal to 1 with the higher value of DID. Note that, in the context of this section, "protecting a NAL unit" means any RTP or network transport mechanism that could improve the probability of success delivery of the packet conveying the NAL unit, including applying a QoS-enabled network, FEC, retransmissions, and advanced scheduling behavior, whenever possible. Wenger, Wang, Schierl Expires June 17, 2008 [Page 13] Internet-Draft RTP Payload Format for SVC Video December 2007 For PRID, the semantics specified in Annex G of [SVC] applies. Note, that MANEs implementing unequal error protection MAY use this information to protect NAL units with smaller PRID values better than those with larger PRID values, for example by including only the more important NAL units in a forward error correction (FEC) protection mechanism. The importance for the decoding process decreases as the PRID value increases. For DID, QID, TID, in addition to the semantics specified in Annex G of [SVC], according to this memo, values of DID, QID, or TID indicate the relative importance in their respective dimension. A lower value of DID, QID, or TID indicates a higher importance if the other two components are identical. MANEs MAY use this information to protect more important NAL units better than less important NAL units. For U, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to protect NAL units with U equal to 1 better than NAL units with U equal to 0. For D, in addition to the semantics specified in Annex G of [SVC], according to this memo, MANEs MAY use this information to determine whether a given NAL unit is required for successfully decoding a certain Operation Point of the SVC bitstream, hence to decide whether to forward the NAL unit. 6.5. Packetization Modes Please see section 5.4 of [RFC3984]. 6.6. Decoding Order Number (DON) Please see section 5.5 of [RFC3984]. The following applies in addition. If different Layers of a SVC bitstream are transported in more than one RTP session, the DON values of all the NAL units in the RTP sessions using interleaved mode MUST indicate CL-DON values. When Session multiplexing is used and at least one STAP-A packet is present in any of the RTP sessions, the following applies. A PACSI NAL unit MUST be present in each STAP-A packet. A CL-DON field MUST be present in the PACSI NAL unit included in each STAP-A. The DON values for the NAL units in each STAP-A packet MUST be derived as follows and indicate CL-DON values. The CL-DON field in the PACSI NAL unit specifies the value of DON for the first NAL unit in the STAP-A in transmission order. For each successive NAL unit in appearance order in the STAP-A, the value of DON is equal to (the value of DON of the previous NAL unit in the STAP-A + 1) % 65536, wherein '%' stands for modulo operation. Wenger, Wang, Schierl Expires June 17, 2008 [Page 14] Internet-Draft RTP Payload Format for SVC Video December 2007 6.7. Aggregation Packets Please see section 5.7 of [RFC3984]. 6.8. Fragmentation Units (FUs) Please see section 5.8 of [RFC3984]. 6.9. Payload Content Scalability Information (PACSI) NAL Unit A new NAL unit type is specified in this memo, and referred to as payload content scalability information (PACSI) NAL unit. The OPTIONAL PACSI NAL unit, if present, MUST be the first NAL unit in an aggregation packet, and it MUST NOT be present in other types of packets. The PACSI NAL unit indicates scalability information and other characteristics that are common for all the remaining NAL units in the payload of the aggregation packet. Furthermore, a PACSI NAL unit MAY contain zero or more SEI NAL units. PACSI NAL unit makes it easier for MANEs to decide whether to forward/process/discard the aggregation packet containing the PACSI NAL unit. Other reasons to use PACSI NAL units are explained later when specifying the semantics of the fields. Senders MAY create PACSI NAL units and receivers MAY ignore them, or use them as hints to enable efficient aggregation packet processing. Note that the NAL unit type for the PACSI NAL unit is selected among those values that are unspecified in [SVC] and [RFC3984]. When the first aggregation unit of an aggregation packet contains a PACSI NAL unit, there MUST be at least one additional aggregation unit present in the same packet. The RTP header and payload header fields of the aggregation packet are set according to the remaining NAL units in the aggregation packet. When a PACSI NAL unit is included in a multi-time aggregation packet (MTAP), the decoding order number (DON) for the PACSI NAL unit MUST be set to indicate that the PACSI NAL unit has an identical DON to the first NAL unit in decoding order among the remaining NAL units in the aggregation packet. The structure of a PACSI NAL unit is as follows. The first four octets are exactly the same as the four-byte SVC NAL unit header as discussed in section 3.3. They are followed by one always present octet, five optional octets, and zero or more SEI NAL units, each SEI NAL unit preceded by a 16-bit unsigned size field (in network byte order) that indicates the size of the following NAL unit in bytes (excluding these two octets, but including the NAL unit type octet of the SEI NAL unit). Figure 1 illustrates the PACSI NAL unit structure and an example of a PACSI NAL unit containing two SEI NAL units. The bits A, P, C, S, and E are specified only if the bit X is equal to 1. The fields TL0PICIDX and IDRPICID are present only if the bit Y is equal to 1. The fields TL0PICIDX and IDRPICID MUST NOT be present if the bit Y is equal to 0. The field CL-DON is present only if the bit T Wenger, Wang, Schierl Expires June 17, 2008 [Page 15] Internet-Draft RTP Payload Format for SVC Video December 2007 is equal to 1. The field T MUST be equal to 0 if the aggregation packet containing the PACSI NAL unit is not an STAP-A packet. 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 |R|I| PRID |N| DID | QID | TID |U|D|O| RR| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|Y|T|A|P|C|S|E| TL0PICIDX (o.)| IDRPICID (o.) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | CL-DON (o.) | NAL unit size 1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SEI NAL unit 1 | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | NAL unit size 2 | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | | SEI NAL unit 2 | | +-+-+-+-+-+-+-+-+-+-+ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1. PACSI NAL unit structure. Fields suffixed by "(o.)" are OPTIONAL. The values of the fields in PACSI NAL unit MUST be set as follows. The F bit MUST be set to 1 if the F bit in at least one of the remaining NAL units in the payload is equal to 1. Otherwise, the F bit MUST be set to 0. The NRI field MUST be set to the highest value of NRI field among all the remaining NAL units in the payload. The Type field MUST be set to 30. o The R bit MUST be set to 1. o The I bit MUST be set to 1 if the I bit of at least one of the remaining NAL units in the payload is equal to 1. Otherwise, the I bit MUST be set to 0. The PRID field MUST be set to the lowest value of the PRID values of all the remaining NAL units in the payload. o The N bit MUST be set to 1 if the N bit of all the remaining NAL units in the payload is equal to 1. Otherwise, the N bit MUST be set to 0. Wenger, Wang, Schierl Expires June 17, 2008 [Page 16] Internet-Draft RTP Payload Format for SVC Video December 2007 o The DID field MUST be set to the lowest value of the DID values of all the remaining NAL units in the payload. o The QID field MUST be set to the lowest value of the QID values of all the remaining NAL units with the lowest value of DID in the payload. o The TID field MUST be set to the lowest value of the TID values of all the remaining NAL units with the lowest value of DID in the payload. o The U bit MUST be set to 1 if the U bit of at least one of the remaining NAL units in the payload is equal to 1. Otherwise, the U bit MUST be set to 0. The D bit MUST be set to 1 if the D value of all the remaining NAL unit in the payload is equal to 1. Otherwise, the D bit MUST be set to 0. o The O bit MUST be set to 1 if the O bit of at least one of the remaining NAL units in the payload is equal to 1. Otherwise, the O bit MUST be set to 0. o The RR field MUST be set to '11' (in binary form). o If the X bit is equal to 1, the bits A, P, C, S, and E are specified as in below. Otherwise, the bits A, P, C, S, and E are unspecified, and receivers MUST ignore these bits. The X bit SHOULD be identical for all the PACSI NAL units involved in all the RTP sessions conveying an SVC bitstream. o If the Y bit is equal to 1, the OPTIONAL fields TL0PICIDX and IDRPICID MUST be present and specified as in below. Otherwise, the fields TL0PICIDX and IDRPICID MUST NOT be present. The Y bit SHOULD be identical for all the PACSI NAL units involved in all the RTP sessions conveying an SVC bitstream. o If the T bit is equal to 1, the OPTIONAL field CL-DON MUST be present and specified as in below. Otherwise, the field CL-DON MUST NOT be present. o The A bit MUST be set to 1 if all the target NAL units belong to anchor layer representations. Otherwise, the A bit MUST be set to 0. The target NAL units are such NAL units contained in the aggregation packet, but not included in the PACSI NAL unit, that are within the access unit to which the first NAL unit following the PACSI NAL unit in the aggregation packet belongs. The A bit SHOULD be identical for all the PACSI NAL units for which the target NAL units belong to the same access unit. Informative note: The A bit indicates whether CGS or spatial layer switching at a non-IDR layer representation (a layer representation with nal_unit_type not equal to 5 and idr_flag not equal to 1) can be Wenger, Wang, Schierl Expires June 17, 2008 [Page 17] Internet-Draft RTP Payload Format for SVC Video December 2007 performed. When the coded pattern like IBBP is in use, non-IDR intra layer representation can be used for random access. Compared to using only IDR layer representations, higher coding efficiency can be achieved. The H.264/AVC or SVC solution to indicate the random accessibility of a non-IDR intra layer representation is using recovery point SEI message. However, with this A bit it is much easier to parse than to parse the recovery point SEI message, which may even be buried deeply in an SEI NAL unit. Furthermore, the SEI message may not be present in the bitstream. o The T bit MUST be set to 1 if all the target NAL units (as defined above) belong to temporal scalable layer switching points. Otherwise, the T bit MUST be set to 0. The T bit SHOULD be identical for all the PACSI NAL units for which the target NAL units belong to the same access unit. Informative note: The T bit indicates whether switching to the next higher temporal layer (i.e. upgrading of frame rate) can be performed at the layer representation. SVC specifies temporal layer switching point SEI message for signaling of temporal layer switching points when needed. However, with this T bit it is much easier to parse than to parse the recovery point SEI message, which may even be buried deeply in an SEI NAL unit. Furthermore, the SEI message may not be present in the bitstream. o The P bit MUST be set to 1 if all the target NAL units (as defined above) are with redundant_pic_cnt greater than 0, i.e. the slices are redundant slices. Otherwise, the P bit MUST be set to 0. The P bit SHOULD be identical for all the PACSI NAL units for which the target NAL units belong to the same access unit. Informative note: The P bit indicates whether the packet can be discarded because it contains redundant slice NAL units. Without this bit, the corresponding information can be concluded from the syntax element redundant_pic_cnt, which is buried in the slice header, which is not in the fixed-length coded NAL unit header. o The C bit MUST be set to 1 if the target NAL units (as defined above) belong to an access unit for which the layer representation having the greatest value of dependency_id among all the layer representations containing the target NAL units is an intra layer representation. Otherwise, the C bit MUST be set to 0. The C bit SHOULD be identical for all the PACSI NAL units for which the target NAL units belong to the same access unit. Informative note: The C bit indicates whether the packet contains intra slices which may be the only packets to be forwarded for a fast forward playback, e.g. when the network condition is extremely bad. o The S bit MUST be set to 1, if the first VCL NAL unit, in decoding order, of the layer representation containing the first NAL unit Wenger, Wang, Schierl Expires June 17, 2008 [Page 18] Internet-Draft RTP Payload Format for SVC Video December 2007 following the PACSI NAL unit in the aggregation packet is present in the payload. Otherwise, the S bit MUST be set to 0. o The E bit MUST be set to 1, if the last VCL NAL unit, in decoding order, of the layer representation containing the first NAL unit following the PACSI NAL unit in the aggregation packet is present in the payload. Otherwise, the E field MUST be set to 0. Informative note: The S or E bit indicates whether the first or last slice, in decoding order, of a layer representation is in the packet, to enable a MANE to detect slice loss and take proper action such as requesting a retransmission as soon as possible, as well as to allow an efficient playout buffer handling similarly as the M bit in the RTP header. The M bit in the RTP header still indicates the end of an access unit, not the end of a layer representation. o When present, the TL0PICIDX field MUST be set to equal to tl0_dep_rep_idx as specified in Annex G of [SVC] for the layer representation containing the first NAL unit following the PACSI NAL unit in the aggregation packet. o When present, the IDRPICID field MUST be set to equal to effective_idr_pic_id as specified in Annex G of [SVC] for the layer representation containing the first NAL unit following the PACSI NAL unit in the aggregation packet. Informative note: The TL0PICIDX and IDRPICID fields enable the detection of the loss of layer representations in the most important temporal layer, by receivers as well as MANEs. SVC includes a solution by using SEI messages, which are harder to parse and may not be present in the bitstream at all. o When present, the field CL-DON indicates the cross-layer decoding order number for the first NAL unit in the STAP-A in transmission order. SEI NAL units included in the PACSI NAL unit, if any, MUST contain a subset of the SEI messages associated with the access unit of the first NAL unit following the PACSI NAL unit within the aggregation packet. Informative note: Senders may repeat such SEI NAL units in the PACSI NAL unit the presence of which in more than one packet is essential for packet loss robustness. Receivers may use the repeated SEI messages in place of missing SEI messages. In H.264/AVC and SVC, within each access unit, SEI NAL units must appear before any VCL NAL unit in decoding order. Therefore, without using PACSI NAL units, SEI messages are typically only conveyed in the first packet of those packets conveying an access unit. An SEI message SHOULD NOT be included in a PACSI NAL unit and included in one of the remaining NAL units contained in the same aggregation packet at the same time. Wenger, Wang, Schierl Expires June 17, 2008 [Page 19] Internet-Draft RTP Payload Format for SVC Video December 2007 7. Packetization Rules Please see section 6 of [RFC3984]. The following rules apply in addition. All receivers MUST support the single NAL unit packetization mode to provide backward compatibility to endpoints supporting only the single NAL unit mode of RFC 3984. However, the single NAL unit packetization mode SHOULD NOT be used whenever possible, because encapsulating NAL units of small sizes, e.g. small NAL units containing parameter sets or SEI messages, in their own packets is typically less efficient because of the relatively big overhead. All receivers MUST support the non-interleaved mode of [RFC3984]. Informative note: The non-interleaved mode allows an application to encapsulate a single NAL unit in a single RTP packet. Historically, the single NAL unit mode has been included into [RFC3984] only for compatibility with ITU-T Rec. H.241 Annex A [H.241]. There is no point in carrying this historic ballast towards a new application space such as the one provided with SVC. More technically speaking, the implementation complexity increase for providing the additional mechanisms of the non-interleaved mode (namely STAP-A) is so minor, and the benefits are so great, that STAP-A implementation is required. A NAL unit of small size SHOULD be encapsulated in an aggregation packet together with one or more other NAL units. For example, non-VCL NAL units such as access unit delimiter, parameter set, or SEI NAL unit are typically small. A prefix NAL unit SHOULD be aggregated to the same packet as the associated NAL unit following the prefix NAL unit in decoding order. Informative note: When either the prefix NAL unit or the associated NAL unit containing an H.264/AVC coded slice is lost, the remaining one would be hardly useful in SVC context, wherein the prefix NAL unit must be available for decoded picture buffer management operations of the decoding process. When the first aggregation unit of an aggregation packet contains a PACSI NAL unit, there MUST be at least one additional aggregation unit present in the same packet. Non-VCL NAL units SHOULD be conveyed in the same session as the associated VCL NAL units. To meet this, SEI messages that are contained in scalable nesting SEI message and are applicable to more than one session SHOULD be separated and contained into multiple scalable nesting SEI messages. The CL-DON values MUST indicate the cross-layer decoding order number values as if all these SEI messages were in separate scalable nesting SEI messages and contained in the beginning of the corresponding access units as specified in [SVC]. Wenger, Wang, Schierl Expires June 17, 2008 [Page 20] Internet-Draft RTP Payload Format for SVC Video December 2007 When Session multiplexing is used, the following applies. The two options I. and II. are available: In all RTP Sessions non-interleaved mode or single NAL unit mode MUST be used and CL-DON MUST NOT be present: If an access unit of sampling time instance X is present in RTP session A, this access unit MUST be also present in any RTP session, which depends on RTP session A. RTP sessions MUST have a one-dimensional dependency structure, i.e. an RTP session can be enhanced by exactly one other RTP session only. M-bit of the RTP header SHALL be set according to [RFC3550], i.e. the end of an access unit MUST be indicated in each of the RTP sessions. All RTP sessions MUST use the same RTP Timestamp scale and MUST use the same RTP timestamp for packets in the different RTP session containing NAL units of the same sampling time instance. At least one of the following parameters MUST be present in the RTP sessions indicating buffering values for each RTP session of the RTP session multiplex: - sprop-prebuf-size - sprop-prebuf-time Informative note: Restriction a. allows only for multiplexing of RTP session with the same frame rate or requires in RTP sessions with higher frame rate also NAL units of the access units, which are also present in RTP sessions which the session in question depends on. An example algorithm for packet and NAL unit reordering is given in 8.1.1. CL-DON MUST be used An RTP session that does not use interleaved mode MUST be constrained as follows. Non-interleaved mode MUST be used. STAP-A MUST be used, and any other type of packets MUST NOT be used. Each STAP-A MUST contain a PACSI NAL unit and the CL-DON field MUST be present in the PACSI NAL unit. Informative note: The motivation for these constraints is to allow the use of non-interleaved mode for the session conveying the H.264/AVC compatible (full) base layer, such that RFC 3984 receivers without interleaved mode implementation can subscribe to the (full) base layer session. 8. De-Packetization Process (Informative) Wenger, Wang, Schierl Expires June 17, 2008 [Page 21] Internet-Draft RTP Payload Format for SVC Video December 2007 For a single RTP session, the de-packetization process specified in section 7 of [RFC3984] applies [with some fixes to section 7 of RFC 3984 and some changes/additions to section 7.3 (Additional De- Packetization Guidelines) of RFC 3984 - TBD]. For receiving more than one of multiple RTP sessions conveying a scalable bitstream, an example of a suitable implementation of the de- packetization process is specified in section 8.1. 8.1. De-Packetization Process for NAL Units Conveyed using Session Multiplexing As for a single RTP session, the general concept behind these de- packetization rules is to reorder NAL units from transmission order to the NAL unit decoding order. In this section, "the RTP sessions" refer to the RTP sessions for which the NAL units are de-packetized. The receiver includes a receiver buffer, which is used to compensate for different session initiation times, transmission delay jitter and to reorder NAL units from transmission order to the NAL unit decoding order. In this section, the receiver operation is described under the assumption that all the RTP sessions initiate at the same time, and there is no transmission delay jitter. However, receivers SHOULD also prepare for both different session initiation times and transmission delay jitter. Receivers can either reserve separate buffers for session initiation variation buffering, transmission delay jitter buffering, and de-session-multiplexing buffering, or use a receiver buffer for all the aforementioned purposes. Moreover, receivers SHOULD take session initiation variation and transmission delay jitter into account in the buffering operation; e.g., by additional initial buffering before starting of decoding and playback. 8.1.1. De-Packetization Process for Session Multiplexing using non- interleaved mode or Single NAL unit mode without the use of CL-DON In this section, NAL unit reordering is described for the constraints of section 7 using the non-interleaved mode or Single NAL unit mode for all RTP sessions, i.e. no CL-DON is used within any of these sessions. The reordering process is based on RTP session dependency, RTP sequence numbers, RTP timestamp and RTP header marker bit. In the following, in-session packet reordering refers to the process of reordering RTP packets according to their sequence number within the receiver buffer of an RTP session. Inter-session packet reordering refers to the process of NAL unit reordering between sessions in case of using Session multiplexing. The following example is used to explain the reordering process. The example refers to three RTP sessions A, B and C as shown in Figure 2. In the example, the dependency signaling as described in 9.2.3, Wenger, Wang, Schierl Expires June 17, 2008 [Page 22] Internet-Draft RTP Payload Format for SVC Video December 2007 indicates, that Session A does not depend on any other of the sessions; B depends on A; C depends on A and B as restricted in section 7. Session A has the lowest frame rate and Session B and C have the same, but a higher frame rate. Informative note: The reordering process described in this subsection can be applied on RTP session with the same or different frame rates. The latter case is only valid, if NAL units of the same time instances of an RTP session are also present in the RTP session which depends on this RTP session. For describing the reordering process no packet loss is assumed. For each of the RTP sessions a receiver buffer according to one of the parameters: sprop-prebuf-size or sprop-prebuf-time is used to buffer RTP packets for each session and in-session packet reordering is applied according to the RTP sequence numbers before starting inter- session packet reordering. sprop-prebuf-size and sprop-prebuf-time should be selected such that buffering each of the sessions according to these parameters allows for an inter-session packet reordering with detection of at least two S0 Synchronization Points, as defined later, in each session. Inter-session packet reordering is started from the lowest RTP session S0. This is the session with the lowest number of dependencies in the one-dimensional dependency tree (in the example: RTP session A). This session is referred to as the lowest session. The session with the next higher number of dependencies is called the next higher session Sn, where n is in the integer rage of 1 and m-1. The highest session Sm-1 is the session with the highest number of dependencies in the one- dimensional dependency tree, where m is the number of RTP sessions in the session multiplex. In the following, a packet loss free transmission is assumed. Starting from Session S0, the first RTP timestamp in the receiver buffer after in-session packet reordering referred to as TS_S0_0_is searched in all the RTP sessions Sn starting with the first packet in each receiver buffer. If TS_S0_0_is found in all sessions, this point is referred to as the S0 Synchronization Point (see Figure 2) If such a point is not found all packets with TS_S0_0 are removed from the receiver buffer of session S0 only. The search as described above is repeated with TS_S0_i until the first S0 Synchronization Point is found, where i gives the counter of RTP timestamps within a RTP session's receiver buffer in RTP sequence number order. Informative note: The RTP timestamp order following the RTP packet order is not the same as the order of increasing RTP timestamp value. A Synchronization Point of session Sn is called the Sn Synchronization Point and defined by matching RTP timestamps in all sessions Sy >= Sn, i.e. TS_Sy_i must be same over the RTP session Sy >= Sn. If the an Sn Synchronization Point is found, that access unit with RTP timestamp TS_Sn_i is restored by depacketizing RTP packets following the rules of Wenger, Wang, Schierl Expires June 17, 2008 [Page 23] Internet-Draft RTP Payload Format for SVC Video December 2007 [RFC3984] starting from session Sn up to Sm-1. The restored NAL units of the sessions are reassembled and place into access unit with RTP timestamp TS_Sn_i in the order of the RTP sessions Sn to Sm-1. Note: Sm-1 does not necessarily have to be the highest available RTP session, but the highest subscribed session using Layered Multicast. When reassembling an access unit for TS_Sn_i Synchronization Point, the packets with TS_Sn_i are removed in RTP sessions Sy >= Sn. After finding the very first S0 Synchronization Point, all RTP packets preceding the TS_S0_i packets in RTP sequence order are removed from the receiver buffers in all sessions. After reassembling a Synchronization Point, the process described above is repeated. Before proceeding to a Synchronization Point in any RTP session starting from the lowest session: If a Synchronization Point is found in any higher session, the access unit represented by such a Synchronization Point has to be reassembled first. Informative note: In case of packet loss, the essential connection between RTP sessions and packets cannot be kept, for that reason, we propose the reduce the reordering process only up to the session which the packet loss contains. After finding a S0 Synchronization point, the reordering can be applied without restrictions. Decoding order and dependency of NAL units per RTP session: C: -(1)---(2)--(3,4)-(5,6)--(7)---(8)-(9,10)(11,12)-(13)--(14)---- | | : : | | : : | | B: -(1,2)-(3,4)-(5)---(6)--(7,8)-(9,10)-(11)-(12)--(13,14)(15,15)- | | | | | | A: -(1)---(2)---------------(3)---(4)---------------(5)----(6)---- -------------------------------------------------------------------> TS: [4] [2] [1] [3] [8] [6] [5] [7] [12] [10] Key: A, B, C - RTP sessions Integer values in '()' - NAL unit decoding order per RTP session '( )' - groups the NAL units of an access unit in an RTP session '|' - indicates layer dependency and the S0 Synchronization Points ':' - indicates layer dependency and the S1 Synchronization Points Integer values in '[]' - RTP Timestamp (TS), sampling time Figure 2. Synchronization Points in Session multiplexing without CL-DON Wenger, Wang, Schierl Expires June 17, 2008 [Page 24] Internet-Draft RTP Payload Format for SVC Video December 2007 8.1.2. De-Packetization Process for Session Multiplexing using CL- DON As present option in section 7, when more than one RTP session is used to convey an SVC Bitstream, for each NAL unit a CL-DON value can be derived. This enables a NAL unit decoding order recovery process without individual deinterleaving process for each RTP session, irrespective of whether any of the sessions uses interleave mode. Excluding the session initiation variation buffer and the transmission delay jitter buffer, the receiver buffer is called the de-session- multiplexing buffer. The de-packetization process for NAL units conveyed in multiple RTP sessions is similar to the single RTP session de-packetization process for interleaved mode as specified in subsection 7.2 of RFC 3984. It is RECOMMENDED to set the size of the de-session-multiplexing buffer, in terms of number of bytes, equal to or greater than the value of the sprop-deint-buf-req media type parameter of the RTP session conveying the SVC Layer for which the decoding requires the presence of the SVC Layers conveyed in all the other RTP sessions, referred to the highest RTP session. There are two buffering states in the receiver: initial buffering and buffering while playing. Initial buffering occurs when the RTP sessions are initialized. After initial buffering, decoding and playback are started, and the buffering-while-playing mode is used. Regardless of the buffering state, the receiver stores incoming NAL units, in reception order, in the de-session-multiplexing buffer as follows. NAL units of aggregation packets are stored in the de- session-multiplexing buffer individually. The value of DON (i.e. CL- 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 9.1 of this specification. o Function don_diff is specified in section 5.5 of RFC 3984. o Constant N is the value of the OPTIONAL sprop-interleaving-depth media type parameter of the highest RTP session 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 de-session-multiplexing buffer. Wenger, Wang, Schierl Expires June 17, 2008 [Page 25] Internet-Draft RTP Payload Format for SVC Video December 2007 o If sprop-max-don-diff of the highest RTP session is present, don_diff(m,n) is greater than the value of sprop-max-don-diff of the highest RTP session, 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 media type parameter of the highest RTP session. The NAL units to be removed from the de-session-multiplexing buffer are determined as follows: o If the de-session-multiplexing buffer contains at least N VCL NAL units, NAL units are removed from the de-session-multiplexing 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 of the highest RTP session is present, all NAL units m for which don_diff(m,n) is greater than sprop-max-don-diff of the highest RTP session are removed from the de-session-multiplexing 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 de-session-multiplexing buffer. The order in which NAL units are passed to the decoder is specified as follows: o Let PDON be a variable that is initialized to 0 at the beginning of the RTP sessions. 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. 9. 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 media type registration for the SVC codec. A mapping of the parameters into the Session Description Protocol (SDP) [RFC4566] is also provided for Wenger, Wang, Schierl Expires June 17, 2008 [Page 26] Internet-Draft RTP Payload Format for SVC Video December 2007 applications that use SDP. Equivalent parameters could be defined elsewhere for use with control protocols that do not use 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. 9.1. Media Type Registration The media subtype for the SVC codec is allocated from the IETF tree. The receiver MUST ignore any unspecified parameter. Informative note: Requiring ignoring unspecified parameter allows for backward compatibility of future extensions. For example, if a future specification that is backward compatible to this specification specifies some new parameters, then a receiver according to this specification is capable of receiving data per the new payload but ignoring those parameters newly specified in the new payload specification. This sentence is also present in RFC 3984. Media Type name: video Media subtype name: H264-SVC or H264 The media subtype "H264" MUST be used for RTP streams using RFC 3984, i.e. not using any of the new features introduced by this specification compared to RFC 3984. [Ed. The new features are to be listed herein.] For RTP streams using any of the new features introduced by this specification compared to RFC 3984, the media subtype "H264-SVC" SHOULD be used, and the media subtype "H264" MAY be used. Use of the media subtype "H264" for RTP streams using the new features allows for RFC 3984 receivers to negotiate and receive H.264/AVC or SVC streams packetized according to this specification, but to ignore media parameters and NAL unit types it does not recognize. Required parameters: none OPTIONAL parameters: profile-level-id: A base16 [RFC3548] (hexadecimal) representation of the following three bytes in the sequence parameter set NAL unit specified in [SVC]: 1) profile_idc, 2) a byte herein referred to as Wenger, Wang, Schierl Expires June 17, 2008 [Page 27] Internet-Draft RTP Payload Format for SVC Video December 2007 profile-iop, composed of the values of constraint_set0_flag, constraint_set1_flag, constraint_set2_flag, constraint_set3_flag, and reserved_zero_4bits in bit-significance order, starting from the most significant bit, and 3) level_idc. Note that reserved_zero_4bits is required to be equal to 0 in [SVC], but 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 [SVC] when it decodes the NAL unit stream. The profile-iop byte indicates whether the NAL unit stream also obeys all the constraints as specified in subsection 7.4.2.1.1 of [SVC]. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session, and all NAL units conveyed in other RTP sessions, if present, the current RTP session depends on. The current RTP session MAY depend on other RTP sessions when a scalable bitstream is transported with more than one RTP session and the current session is not an independent RTP session. 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 signaled with the profile-iop byte 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 Wenger, Wang, Schierl Expires June 17, 2008 [Page 28] Internet-Draft RTP Payload Format for SVC Video December 2007 be used (section 10.2 of [RFC4566]). 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: [Ed. If these parameters may also be used to signal properties of a NAL unit stream, as in 8.2.2 of RFC 3984, which is contradictory with the semantics, then we need to say that the NAL unit stream is the one containing also those from the RTP sessions (if present) the current depends on. Furthermore, then for max-br, it might be useful to have two versions, one for the current session only, and one for the current session and the sessions it depends on.] These parameters MAY be used to signal the capabilities of a receiver or a sender 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. 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. 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 Wenger, Wang, Schierl Expires June 17, 2008 [Page 29] Internet-Draft RTP Payload Format for SVC Video December 2007 level specified in the value of the profile- level-id parameter, if the receiver can support all the properties of level A. Informative note: When the OPTIONAL media 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 or Table G-n of [SVC] 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 or Table G-n of [SVC]. 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 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 or Table G-n of [SVC] 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 or Table G-n of [SVC]. Senders MAY use this knowledge to send larger pictures at a proportionally lower frame rate than is Wenger, Wang, Schierl Expires June 17, 2008 [Page 30] Internet-Draft RTP Payload Format for SVC Video December 2007 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 or G.n item m of [SVC]) and in units of 1200 bits for the NAL HRD parameters (see A.3.1 item j or G.n item m of [SVC]). 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 or Table G-n of [SVC] 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 or Table G-n of [SVC]. 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 or Table G-n of [SVC]. Informative note: The coded picture buffer is used in the hypothetical reference decoder (Annex C) of SVC. The use of the hypothetical reference decoder is recommended in SVC 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 SVC, 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 Wenger, Wang, Schierl Expires June 17, 2008 [Page 31] Internet-Draft RTP Payload Format for SVC Video December 2007 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 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 or Table G-n of [SVC] 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 [SVC]. The value of max-dpb MUST be greater than or equal to the value of MaxDPB for the level given in Table A-1 or Table G-n of [SVC]. 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 or G.n item m of [SVC]) and in units of 1200 bits per second for the NAL HRD parameters (see A.3.1 item j or G.n item m of [SVC]). The max-br parameter signals that the video Wenger, Wang, Schierl Expires June 17, 2008 [Page 32] Internet-Draft RTP Payload Format for SVC Video December 2007 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: o The value of max-br replaces the MaxBR value of the signaled level (in Table A-1 of or Table G-n of [SVC]). o When the max-cpb parameter is not present, the result of the following formula replaces the value of MaxCPB in Table A-1 or Table G-n of [SVC]: (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 or Table G-n of [SVC]. Senders MAY use this knowledge to send higher bitrate video as allowed in the level definition of SVC, 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 Wenger, Wang, Schierl Expires June 17, 2008 [Page 33] Internet-Draft RTP Payload Format for SVC Video December 2007 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 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 be placed in the NAL unit stream to precede any other NAL units in decoding order by the receiver. The parameter MUST NOT be used to indicate codec capability in any capability exchange procedure. The value of the parameter is the base64 [RFC3548] representation of the initial Wenger, Wang, Schierl Expires June 17, 2008 [Page 34] Internet-Draft RTP Payload Format for SVC Video December 2007 parameter set NAL units as specified in sections 7.3.2.1, 7.3.2.2 and G.7.3.2.1.3 of [SVC]. 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. parameter-add: This parameter MAY be used to signal whether the receiver of this parameter is allowed to add parameter sets in its signaling response using the sprop-parameter-sets media parameter. The value of this parameter is either 0 or 1. 0 is equal to false; i.e., it is not allowed to add parameter sets. 1 is equal to true; i.e., it is allowed to add parameter sets. If the parameter is not present, its value MUST be 1. 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 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 [H.241] (see section 12.1 of RFC 3984). When the value of Wenger, Wang, Schierl Expires June 17, 2008 [Page 35] Internet-Draft RTP Payload Format for SVC Video December 2007 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 the current RTP session does not depend on any other RTP session, and packetization-mode is not present or the value of packetization-mode is equal to 0 or 1. This parameter MUST be present when the the current RTP session depends on any other RTP session or the value of packetization-mode is equal to 2. This parameter signals the properties of a NAL unit stream. It specifies the maximum number of VCL NAL units that precede any VCL NAL unit in the NAL unit 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. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session, and all NAL units conveyed in other RTP sessions, if present, the current RTP session depends on. 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 the current RTP session does not depend on any other RTP session, and packetization-mode is not present or the value of packetization-mode is equal to 0 or 1. This parameter MUST be present when the the current RTP session depends on any other RTP session or the value of packetization-mode is equal to 2. sprop-deint-buf-req signals the required size of the deinterleaving buffer for the NAL unit stream. The value of the parameter MUST be Wenger, Wang, Schierl Expires June 17, 2008 [Page 36] Internet-Draft RTP Payload Format for SVC Video December 2007 greater than or equal to the maximum buffer occupancy (in units of bytes) required in such a deinterleaving buffer that is specified in section 8 of this specification. It is guaranteed that receivers can perform the deinterleaving of interleaved NAL units into NAL unit decoding order, when the deinterleaving buffer size is at least the value of sprop-deint-buf-req in terms of bytes. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session, and all NAL units conveyed in other RTP sessions, if present, the current RTP session depends on. 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. When a scalable bitstream is conveyed in more than one RTP session, and the sessions initiates at different time, the session initiation variation has also to be compensated by an appropriately sized buffer. 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, and that the 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. Wenger, Wang, Schierl Expires June 17, 2008 [Page 37] Internet-Draft RTP Payload Format for SVC Video December 2007 sprop-init-buf-time: This parameter MAY be used to signal the properties of a NAL unit stream. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session, and all NAL units conveyed in other RTP sessions, if present, the current RTP session depends on. The parameter signals the initial buffering time for a receiver before starting to recover the NAL unit decoding order from the transmission order. 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. 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 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- Wenger, Wang, Schierl Expires June 17, 2008 [Page 38] Internet-Draft RTP Payload Format for SVC Video December 2007 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. Yet another aspect receivers SHOULD take into account is the session initiation variation when a scalable bitstream is conveyed in more than one session, including buffering the variation. sprop-max-don-diff: This parameter MAY be used to signal the properties of a NAL unit stream. It MUST NOT be used to signal transmitter or receiver or codec capabilities. 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. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session, and all NAL units conveyed in other RTP sessions, if present, the current RTP session depends on. 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 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), Wenger, Wang, Schierl Expires June 17, 2008 [Page 39] Internet-Draft RTP Payload Format for SVC Video December 2007 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 6.6 of this specification. 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 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 Wenger, Wang, Schierl Expires June 17, 2008 [Page 40] Internet-Draft RTP Payload Format for SVC Video December 2007 negative impact. sprop-prebuf-size: With this parameter, CL-DON MUST NOT be present in the current RTP session. This parameter MUST be present when the the current RTP session depends on any other RTP session. sprop-prebuf-size signals the required size of the receiver buffer for the NAL unit stream. It is guaranteed that receivers can perform the inter-session packet reordering as described in section 8.1.1 into NAL unit decoding order, when the receiver buffer size is at least the value of sprop-prebuf-size in terms of bytes. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session, The value of sprop-prebuf-size MUST be an integer in the range of 0 to 4294967295, inclusive. Informative note: sprop-prebuf-size indicates the required size of the prebuffering receiver buffer only. When network jitter can occur, an appropriately sized jitter buffer has to be provisioned for as well. When a scalable bitstream is conveyed in more than one RTP session, and the sessions initiates at different time, the session initiation variation has also to be compensated by an appropriately sized buffer. sprop-prebuf-time: With this parameter, CL-DON MUST NOT be present in the current RTP session. This parameter MAY be used to signal the properties of a NAL unit stream within a session multiplexing. Herein the NAL unit stream refers to the one consisting of all NAL units conveyed in the current RTP session. The parameter signals the initial buffering time is used for a receiver before starting to recover the NAL unit decoding order from the transmission order. 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. 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-prebuf-time MUST be an integer in the range of 0 to 4294967295, inclusive. In addition to the signaled sprop-prebuf-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. Yet another aspect receivers SHOULD take into account is the session initiation Wenger, Wang, Schierl Expires June 17, 2008 [Page 41] Internet-Draft RTP Payload Format for SVC Video December 2007 variation when a scalable bitstream is conveyed in more than one session, including buffering the variation. sprop-scalability-info: This parameter MAY be used to convey the NAL unit containing the scalability information SEI message as specified in Annex G of [SVC]. This parameter MAY be used to signal the contained Layers of an SVC bitstream. The parameter MUST NOT be used to indicate codec capability in any capability exchange procedure. The value of the parameter is the base64 representation of the NAL unit containing the scalability information SEI message. If present, the NAL unit MUST contain only a scalability information SEI message. This parameter MAY be used in an offering or declarative SDP message to indicate what Layers can be provided. A receiver MAY indicate its choice of one Layer using the optional media type parameter scalable- layer-id. sprop-layer-range: This parameter MAY be used to signal two sets of the layer identification values of the lowest and highest operation points conveyed in the RTP session. Each set is a base16 representation of a three-character value, with the first character representing DID, the second character representing QID, and the third character representing TID. The two sets are comma separated. Let DIDl and DIDh be the least DID value and the greatest DID value, respectively, among all the NAL units conveyed in the RTP session. Let QIDl and TIDl be the least QID value and the least TID value, respectively, among all the NAL units that are conveyed in the RTP session and that have DID equal to DIDl. Let QIDh and TIDh be the greatest QID value and the great TID value, respectively, among all the NAL units that are conveyed in the RTP session and that have DID equal to DIDh. The first set indicates the DID, QID and TID values of the lowest operation point, for which the DID, QID and TID values are equal to DIDl, QIDl, and TIDl, respectively. The second set indicates the DID, QID and TID values of the highest operation point, for which the DID, QID and TID values are equal to DIDh, QIDh, and TIDh, respectively. scalable-layer-id: This parameter MAY be used to signal a receiver's choice of the offers or declared Operation Points or Layers using sprop-scalability-info. The value of scalable-layer-id is a base16 representation of the layer_id[ i ] syntax element in the scalability information SEI message as specified in [SVC]. sprop-spatial-resolution: [Ed. I know that framerate and bitrate SDP parameters are already available, but failed to find a spatial resolution SDP parameter. It would be good if this is already defined. Otherwise, it would be better to be defined somewhere else because it is a generic parameter.] Wenger, Wang, Schierl Expires June 17, 2008 [Page 42] Internet-Draft RTP Payload Format for SVC Video December 2007 This parameter MAY be used to indicate the property of a stream or the capability of a receiver or sender implementation. The value is a base16 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 10 of RFC XXXX. Public specification: Please refer to RFC XXXX and its section 14. Additional information: None File extensions: none Macintosh file type code: none Object identifier or OID: none Person & email address to contact for further information: Intended usage: COMMON Author: Change controller: IETF Audio/Video Transport working group delegated from the IESG. 9.2. SDP Parameters [Ed. For agreeing on a Layer or OP in unicast, an SDP can contain multiple m lines with bitrate, framerate and spatial resolution parameters available, in addition to sprop-scalability-info. The receive can select one of the m lines, or, for operation points that are not included in the m lines, one of the "scalable layers" specified by sprop-scalabiltiy-info using scalable-layer-id. For layered multicast, then the grouping signaling in [I-D.ietf-mmusic- decoding-dependency] is needed. The above would conveniently support also the normal ROI use cases (with a few ROIs each indicated as a "scalable layer") but not the interactive ROI use cases. The quality layer using priority_id use cases are not supported either. That would need one more optional media type parameter, to identify a quality layer. The lightweight transcoding use cases should be supported well by using (multiple) normal AVC SDP offering messages. ] Wenger, Wang, Schierl Expires June 17, 2008 [Page 43] Internet-Draft RTP Payload Format for SVC Video December 2007 9.2.1. Mapping of Payload Type Parameters to SDP The media type video/H264-SVC string is mapped to fields in the Session Description Protocol (SDP) as follows: The media name in the "m=" line of SDP MUST be video. The encoding name in the "a=rtpmap" line of SDP MUST be H264-SVC (the media subtype). The clock rate in the "a=rtpmap" line MUST be 90000. The OPTIONAL parameters "profile-level-id", "max-mbps", "max-fs", "max-cpb", "max-dpb", "max-br", "redundant-pic-cap", "sprop-parameter-sets", "parameter-add", "packetization-mode", "sprop-interleaving-depth", "deint-buf-cap", "sprop-deint-buf-req", "sprop-init-buf-time", "sprop-max-don-diff", "max-rcmd-nalu-size", "sprop-prebuf-size", "sprop-prebuf-time", "sprop-layer-range", "sprop-scalability-info", "scalable-layer-id", and "sprop-spatial-resolution", when present, MUST be included in the "a=fmtp" line of SDP. These parameters are expressed as a media type string, in the form of a semicolon separated list of parameter=value pairs. 9.2.2. Usage with the SDP Offer/Answer Model When H.264 or SVC is offered over RTP using SDP in an Offer/Answer model [RFC3264] for negotiation for unicast usage, the following limitations and rules apply: o The parameters identifying a media format configuration for H.264 or SVC are "profile-level-id", "packetization-mode", and, if required by "packetization-mode", "sprop-deint-buf-req". These three parameters 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. Informative note: The requirement for symmetric use applies only for the above three parameters and not for the other stream properties and capability parameters. 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 [RFC3264]. 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. Informative note: An offerer, when receiving the answer, has to compare payload types not declared in the offer based on media type (i.e., Wenger, Wang, Schierl Expires June 17, 2008 [Page 44] Internet-Draft RTP Payload Format for SVC Video December 2007 video/H264-SVC) and the above three 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. An answerer MAY select from the layers offered in the "sprop- scalability-information" parameter by including "scalable-layer-id" or "scalable-layer-id" in the answer.[Ed. do we need to additionally define behavior with snd/rcvonly parameter?] o The parameters "sprop-parameter-sets", "sprop-deint-buf-req", "sprop-interleaving-depth", "sprop-max-don-diff", "sprop-init-buf- time", "sprop-prebuf-size", "sprop-prebuf-time", "sprop-scalability- information", "sprop-layer-range" describe the properties of the NAL unit 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 or SVC, 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 then 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. 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. o As specified above, an offerer has to include the size of the deinterleaving buffer in the offer for an interleaved H.264 or SVC 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. o The "sprop-parameter-sets" parameter is used as described above. In addition, an answerer MUST maintain all parameter sets received in the offer in its answer. Depending on the value of the "parameter-add" parameter, different rules apply: If "parameter-add" is false (0), the answer MUST NOT add any additional parameter sets. If "parameter-add" Wenger, Wang, Schierl Expires June 17, 2008 [Page 45] Internet-Draft RTP Payload Format for SVC Video December 2007 is true (1), the answerer, in its answer, MAY add additional parameter sets to the "sprop-parameter-sets" parameter. The answerer MUST also, independent of the value of "parameter-add", accept to receive a video stream using the sprop-parameter-sets it declared in the answer. Informative note: care must be taken when parameter sets are added not to cause overwriting of already transmitted parameter sets by using conflicting parameter set identifiers. For streams being delivered over multicast, the following rules apply in addition: o The stream properties parameters ("sprop-parameter-sets", "sprop- deint-buf-req", "sprop-interleaving-depth", "sprop-max-don-diff", "sprop-init-buf-time", "sprop-prebuf-size", "sprop-prebuf-time", "sprop-scalability-information", and "sprop-layer-range") 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 Wenger, Wang, Schierl Expires June 17, 2008 [Page 46] Internet-Draft RTP Payload Format for SVC Video December 2007 - sprop-max-don-diff - sprop-init-buf-time - sprop-prebuf-size - sprop-prebuf-time - sprop-scalability-information - sprop-layer-range - scalable-layer-id Declaring receiver implementation capabilities: - max-mbps - max-fs - max-cpb - max-dpb - max-br - redundant-pic-cap - deint-buf-cap - max-rcmd-nalu-size Declaring how Offer/Answer negotiation shall be performed: - parameter-add 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 - sprop-prebuf-size - sprop-prebuf-time - sprop-scalability-information - sprop-layer-range - sprop-spatial-resoltuion Declaring the capabilities of the sender when it receives a stream: - max-mbps - max-fs - max-cpb - max-dpb - max-br - redundant-pic-cap - deint-buf-cap Wenger, Wang, Schierl Expires June 17, 2008 [Page 47] Internet-Draft RTP Payload Format for SVC Video December 2007 - max-rcmd-nalu-size Declaring how Offer/Answer negotiation shall be performed: - parameter-add 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/lesser 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. 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 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. 9.2.3. Usage with Session Multiplexing If Session multiplexing is used, the rules on signaling media decoding dependency in SDP as defined in [I-D.ietf-mmusic-decoding-dependency] apply. Wenger, Wang, Schierl Expires June 17, 2008 [Page 48] Internet-Draft RTP Payload Format for SVC Video December 2007 9.2.4. Usage in Declarative Session Descriptions When H.264 or SVC over RTP is offered with SDP in a declarative style, as in RTSP [RFC2326] or SAP [RFC2974], the following considerations are necessary. o All parameters capable of indicating the properties of both a NAL unit stream and a receiver are used to indicate the properties of a NAL unit 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 properties: - profile-level-id - sprop-parameter-sets - packetization-mode - sprop-interleaving-depth - sprop-deint-buf-req - sprop-max-don-diff - sprop-init-buf-time - sprop-prebuf-size - sprop-prebuf-time - sprop-layer-range - sprop-spatial-resolution - sprop-scalability-info Not usable: - max-mbps - max-fs - max-cpb - max-dpb - max-br - redundant-pic-cap - max-rcmd-nalu-size - parameter-add - deint-buf-cap - scalable-layer-id 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. 9.3. Examples 9.3.1. Example for offering a single SVC session Wenger, Wang, Schierl Expires June 17, 2008 [Page 49] Internet-Draft RTP Payload Format for SVC Video December 2007 m = video 20000 RTP/AVP 96 97 98 a = rtpmap:96 AVC/90000 a = fmtp:97 profile-level-id=4d400a; packetization-mode=1; \ sprop-parameter-sets=Z01ACprLFicg,aP4Eag= =; a = rtpmap:97 SVC/90000 a = fmtp:97 profile-level-id=53000c; packetization-mode=1; \ sprop-parameter-sets=Z01ACprLFicg,Z1MADEsA1NZYWCWQ,aP4Eag==, \ aEvgRqA=,aGvgRiA=; a = rtpmap:98 SVC/90000 a = fmtp:98 profile-level-id=53000c; packetization-mode=2; \ init-buf-time=156320; sprop-parameter-sets=Z01ACprLFicg, \ Z1MADEsA1NZYWCWQ,aP4Eag= =,aEvgRqA=,aGvgRiA=; 9.3.2. Example for offering session multiplexing m = video 20000 RTP/AVP 96 97 a = rtpmap:96 H264/90000 a = fmtp:96 profile-level-id=4d400a; packetization-mode=2; \ init-buf-time=156320; sprop-parameter-sets=Z01ACprLFicg,aP4Eag==; a = rtpmap:97 SVC/90000 a = fmtp:97 profile-level-id=53000c; packetization-mode=2; \ init-buf-time=156320; sprop-parameter-sets=Z01ACprLFicg, \ Z1MADEsA1NZYWCWQ,aP4Eag= =,aEvgRqA=,aGvgRiA=; a = mid:1 m = video 20002 RTP/AVP 98 a = rtpmap:98 SVC/90000 a = fmtp:98 profile-level-id=53000c; packetization-mode=2; \ init-buf-time=156320; sprop-parameter-sets=Z01ACprLFicg, \ Z1MADEsA1NZYWCWQ,aP4Eag= =,aEvgRqA=,aGvgRiA=; a = mid:2 a = depend:98 lay 1:96 9.4. Parameter Set Considerations Please see section 8.4 of [RFC3984]. 10. Security Considerations Section 9 of [RFC3984] applies. Additionally, the following applies. Decoders MUST exercise caution with respect to the handling of reserved NAL unit types and reserved SEI messages, particularly if they contain active elements, and MUST restrict their domain of applicability to the presentation containing the stream. The safest way is to simply discard these NAL units and SEI messages. When integrity protection is applied, care MUST be taken that the stream being transported may be scalable; hence a receiver may be able to access only part of the entire stream. Wenger, Wang, Schierl Expires June 17, 2008 [Page 50] Internet-Draft RTP Payload Format for SVC Video December 2007 Informative note: Other security aspects, including confidentiality, authentication, and denial-of-service threat, for SVC are similar as H.264/AVC, as discussed in section 9 of [RFC3984]. 11. Congestion Control Within any given RTP session carrying payload according to this specification, the provisions of section 12 of [RFC3984] apply. Reducing the session bandwidth is possible by one or more of the following means, listed in an order that, in most cases, will assure the least negative impact to the user experience: within the highest Layer identified by the DID field, utilize the TID and/or QID fields in the NAL unit header to drop NAL units with lower importance for the decoding process or human perception. drop all NAL units belonging to the highest enhancement Layer as identified by the highest DID value. dropping NAL units according to their importance for the decoding process, as indicated by the fields in the NAL unit header of the NAL units or in the prefix NAL units. dropping NAL units or entire packets not according to the aforementioned rules (media-unaware stream thinning). This results in the reception of a non-compliant bitstream and, most likely, in very annoying artifacts Informative note: The discussion above is centered on NAL units and not on packets, primarily because that is the level where senders can meaningfully manipulate the scalable bitstream. The mapping of NAL units to RTP packets is fairly flexible when using aggregation packets. Depending on the nature of the congestion control algorithm, the "dimension" of congestion measurement (packet count or bitrate) and reaction to it (reducing packet count or bitrate or both) can be adjusted accordingly. All aforementioned means are available to the RTP sender, regardless whether that sender is located in the sending endpoint or in a mixer based MANE. When a translator-based MANE is employed, then the MANE MAY manipulate the session only on the MANE's outgoing path, so that the sensed end- to-end congestion falls within the permissible envelope. As all translators, in this case the MANE needs to rewrite RTCP RRs to reflect the manipulations it has performed on the session. Informative note: Applications MAY also implement, in addition or separately, other congestion control mechanisms, e.g. as described in [RFC3450] and [Yan]. 12. IANA Consideration [Edt. Note: A new media type should be registered from IANA.] Wenger, Wang, Schierl Expires June 17, 2008 [Page 51] Internet-Draft RTP Payload Format for SVC Video December 2007 13. Informative Appendix: Application Examples 13.1. Introduction Scalable video coding is a concept that has been around at least since MPEG-2 [MPEG2], which goes back as early as 1993. Nevertheless, it has never gained wide acceptance; perhaps partly because applications didn't materialize in the form envisioned during standardization. MPEG and JVT, respectively, performed a requirement analysis before the SVC project was launched. Dozens of scenarios have been studied. While some of the scenarios appear not to follow the most basic design principles of the Internet, e.g. as discussed in section 13.5, -- and are therefore not appropriate for IETF standardization -- others are clearly in the scope of IETF work. Of these, this draft chooses the following subset for immediate consideration. Note that we do not reference the MPEG and JVT documents directly; partly, because at least the MPEG documents have a limited lifespan and are not publicly available, and partly because the language used in these documents is inappropriately video centric and imprecise, when it comes to protocol matters. With these remarks, we now introduce three main application scenarios that we consider as relevant, and that are implementable with this specification. 13.2. Layered Multicast This well-understood form of the use of layered coding [McCanne] implies that all layers are individually conveyed in their own RTP packet streams, each carried in its own RTP session using the IP (multicast) address and port number as the single demultiplexing point. Receivers "tune" into the layers by subscribing to the IP multicast, normally by using IGMP [IGMP]. Layered Multicast has the great advantage of simplicity and easy implementation. However, it has also the great disadvantage of utilizing many different transport addresses. While we consider this not to be a major problem for a professionally maintained content server, receiving client endpoints need to open many ports to IP multicast addresses in their firewalls. This is a practical problem from a firewall and network address translation (NAT) viewpoint. Furthermore, even today IP multicast is not as widely deployed as many wish. We consider layered multicast an important application scenario for the following reasons. First, it is well understood and the implementation constraints are well known. Second, there may well be large scale IP networks outside the immediate Internet context that may wish to employ layered multicast in the future. One possible example could be a combination of content creation and core-network distribution for the Wenger, Wang, Schierl Expires June 17, 2008 [Page 52] Internet-Draft RTP Payload Format for SVC Video December 2007 various mobile TV services, e.g. those being developed by 3GPP (MBMS) [MBMS] and DVB (DVB-H) [DVB-H]. 13.3. Streaming of an SVC scalable stream In this scenario, a streaming server has a repository of stored SVC coded layers for a given content. At the time of streaming, and according to the capabilities, connectivity, and congestion situation of the client(s), the streaming server generates and serves a scalable stream. Both unicast and multicast serving is possible. At the same time, the streaming server may use the same repository of stored layers to compose different streams (with a different set of layers) intended for other audiences. As every endpoint receives only a single SVC RTP session, the number of firewall pinholes can be optimized to one. The main difference between this scenario and straightforward simulcasting lies in the architecture and the requirements of the streaming server, and is therefore out of the scope of IETF standardization. However, compelling arguments can be made why such a streaming server design makes sense. One possible argument is related to storage space and channel bandwidth. Another is bandwidth adaptability without transcoding -- a considerable advantage in a congestion controlled network. When the streaming server learns about congestion, it can reduce sending bitrate by choosing fewer layers, when composing the layered stream; see section 11. SVC is designed to gracefully support both bandwidth rampdown and bandwidth rampup with a considerable dynamic range. This payload format is designed to allow for bandwidth flexibility in the mentioned sense. While, in theory, a transcoding step could achieve a similar dynamic range, the computational demands are impractically high and video quality is typically lowered -- therefore, few (if any) streaming servers implement full transcoding. 13.4. Multicast to MANE, SVC scalable stream to endpoint This scenario is a bit more complex, and designed to optimize the network traffic in a core network, while still requiring only a single pinhole in the endpoint's firewall. One of its key applications is the mobile TV market. Consider a large private IP network, e.g. the core network of 3GPP. Streaming servers within this core network can be assumed to be professionally maintained. We assume that these servers can have many ports open to the network and that layered multicast is a real option. Therefore, we assume that the streaming server multicasts SVC scalable layers, instead of simulcasting different representations of the same content at different bit rates. Also consider many endpoints of different classes. Some of these endpoints may not have the processing power or the display size to Wenger, Wang, Schierl Expires June 17, 2008 [Page 53] Internet-Draft RTP Payload Format for SVC Video December 2007 meaningfully decode all layers; others may have these capabilities. Users of some endpoints may not wish to pay for high quality and are happy with a base service, which may be cheaper or even free. Other users are willing to pay for high quality. Finally, some connected users may have a bandwidth problem in that they can't receive the bandwidth they would want to receive -- be it through congestion, connectivity, change of service quality, or for whatever other reasons. However, all these users have in common that they don't want to be exposed too much, and therefore the number of firewall pinholes need to be small. This situation can be handled best by introducing middleboxes close to the edge of the core network, which receive the layered multicast streams and compose the single SVC scalable bit stream according to the needs of the endpoint connected. These middleboxes are called MANEs throughout this specification. In practice, we envision the MANE to be part of (or at least physically and topologically close to) the base station of a mobile network, where all the signaling and media traffic necessarily are multiplexed on the same physical link. This is why we do not worry too much about decomposition aspects of the MANE as such. MANEs necessarily need to be fairly complex devices. They certainly need to understand the signaling, so, for example, to associate the PT octet in the RTP header with the SVC payload type. A MANE may aggregate multiple RTP streams, possibly from multiple RTP sessions, thus to reduce the number of firewall pinholes required at the endpoints. This type of MANEs is conceptually easy to implement and can offer powerful features, primarily because it necessarily can "see" the payload (including the RTP payload headers), utilize the wealth of layering information available therein, and manipulate it. While such an MANE operation in its most trivial form (combining multiple RTP packet streams into a single one) can be implemented comparatively simply -- reordering the incoming packets according to the DON and sending them in the appropriate order -- more complex forms can also be envisioned. For example, a MANE can be optimizing the outgoing RTP stream to the MTU size of the outgoing path by utilizing the aggregation and fragmentation mechanisms of this memo. A MANE can also perform stream thinning, so to adhere to congestion control principles as discussed in section 11. While the implementation of the forward (media) channel of such a MANE appears to be comparatively simple, the need to rewrite RTCP RRs makes even such a MANE a complex device. While the implementation complexity of either case of a MANE, as discussed above, is fairly high, the computational demands are comparatively low. In particular, SVC and/or this specification contain means to easily generate the correct inter-layer decoding order of NAL units. No serious bit-oriented processing is required and no Wenger, Wang, Schierl Expires June 17, 2008 [Page 54] Internet-Draft RTP Payload Format for SVC Video December 2007 significant state information (beyond that of the signaling and perhaps the SVC sequence parameter sets) need to be kept. Scenarios currently not considered for being unaligned with IP philosophy Remarks have been made that the current draft does not take into consideration at least one application scenario which some JVT folks considered important. In particular, their idea was to make the RTP payload format (or the media stream itself) self-contained enough that a stateless, non-signaling-aware device can "thin" an RTP session to meet the bandwidth demands of the endpoint. They called this device a "Router" or "Gateway", and sometimes a MANE. Obviously, it's not a Router or Gateway in the IETF sense. To distinguish it from a MANE as defined in RFC 3984 and in this specification, let's call it an MDfH (Magic Device from Heaven). To simplify discussions, let's assume point-to-point traffic only. The endpoint has a signaling relationship with the streaming server, but it is known that the MDfH is somewhere in the media path (e.g. because the physical network topology ensures this). It has been requested, at least implicitly through MPEG's and JVT's requirements document, that the MDfH should be capable to intercept the SVC scalable bit stream, modify it by dropping packets or parts thereof, and forwarding the resulting packet stream to the receiving endpoint. It has been requested that this payload specification contains protocol elements facilitating such an operation, and the argument has been made that the NRI field of RFC 3984 serves exactly the same purpose. The authors of this I-D do not consider the scenario above to be aligned with the most basic design philosophies the IETF follows, and therefore have not addressed the comments made (except through this section). In particular, we see the following problems with the MDfH approach): As the very minimum, the MDfH would need to know which RTP streams are carrying SVC. We don't see how this could be accomplished but by using a static payload type. None of the IETF defined RTP profiles envision static payload types for SVC, and even the de-facto profiles developed by some application standard organizations (3GPP for example) do not use this outdated concept. Therefore, the MDfH necessarily needs to be at least "listening" to the signaling. If the RTP packet payload were encrypted, it would be impossible to interpret the payload header and/or the first bytes of the media stream. We understand that there are crypto schemes under discussion that encrypt only the last n bytes of an RTP payload, but we are more than unsure that this is fully in line with the IETF's security vision. Even if the above two problems would have been overcome through standardization outside of the IETF, we still foresee serious design flaws: Wenger, Wang, Schierl Expires June 17, 2008 [Page 55] Internet-Draft RTP Payload Format for SVC Video December 2007 An MDfH can't simply dump RTP packets it doesn't want to forward. It either needs to act as a full RTP Translator (implying that it rewrites RTCP RRs and such), or it needs to patch the RTP sequence numbers to fulfill the RTP specification. Not doing either would, for the receiver, look like the gaps in the sequence numbers occurred due to unintentional erasures, which has interesting effects on congestion control (if implemented), will break pretty much every meta-payload ever developed, and so on. (Many more points could be made here). In summary, based on our current knowledge we are not willing to specify protocol mechanisms that support an operation point that has so little in common with classic RTP use. 13.6. SSRC Multiplexing The authors have played with the idea of introducing SSRC multiplexing, i.e. allowing sending multiple RTP packet streams containing layers in the same RTP session, differentiated by SSRC values. Our intention was to minimize the number of firewall pinholes in an endpoint to one, by using MANEs to aggregate multiple outgoing sessions stemming from a server into a single session (with SSRC multiplexed packet streams). We were hoping that would be feasible even with encrypted packets in an SRTP context. While an implementation along these lines indeed appears to be feasible for the forward media path, the RTCP RR rewrite cannot be implemented in the way necessary for this scheme to work. This relates to the need to authenticate the RTCP RRs as per SRTP [RFC3711]. While the RTCP RR itself does not need to be rewritten by the scheme we envisioned, its transport addresses needs to be manipulated. This, in turn, is incompatible with the mandatory authentication of RTCP RRs. As a result, there would be a requirement that a MANE needs to be in the RTCP security context of the sessions, which was not envisioned in our use case. As the envisioned use case cannot be implemented, we refrained to add the considerable document complexity to support SSRC multiplexing herein. 14. References 14.1. Normative References [H.264] ITU-T Recommendation H.264, "Advanced video coding for generic audiovisual services", Version 4, July 2005. [I-D.ietf-mmusic-decoding-dependency] Schierl, T., and Wenger, S., "Signaling media decoding dependency in Session Description Protocol (SDP)", draft-ietf-mmusic-decoding-dependency-00 (work in progress), November 2007. [MPEG4-10] ISO/IEC International Standard 14496-10:2005. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Wenger, Wang, Schierl Expires June 17, 2008 [Page 56] Internet-Draft RTP Payload Format for SVC Video December 2007 Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model With Session Description Protocol (SDP)", RFC 3264, June 2002. [RFC3548] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 3548, July 2003. [RFC3550] Schulzrinne, H., Casner, S., Frederick, R., and Jacobson, V., "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [RFC3984] Wenger, S., Hannuksela, M., Stockhammer, T., Westerlund,M., and Singer, D., "RTP Payload Format for H.264 Video", RFC 3984, February 2005. [RFC4566] Handley, M., Jacobson, V., and Perkins, C., "SDP: Session Description Protocol", RFC 4566, July 2006. [SVC] Joint Video Team, "Joint Draft 11 of SVC Amendment", available from http://ftp3.itu.ch/av-arch/jvt-site /2007_06_Geneva/JVT-X201.zip, Geneva, Switzerland, June 2007. 14.2. Informative References [DVB-H] DVB - Digital Video Broadcasting (DVB); DVB-H Implementation Guidelines, ETSI TR 102 377, 2005. ITU-T Rec. H.241, "Extended video procedures and control signals for H.300-series terminals", May 2006. [IGMP] Cain, B., Deering S., Kovenlas, I., Fenner, B., and Thyagarajan, A., "Internet Group Management Protocol, Version 3", RFC 3376, October 2002. [McCanne] McCanne, S., Jacobson, V., and Vetterli, M., "Receiver- driven layered multicast", in Proc. of ACM SIGCOMM'96, pages 117--130, Stanford, CA, August 1996. [MBMS] 3GPP - Technical Specification Group Services and System Aspects; Multimedia Broadcast/Multicast Service (MBMS); Protocols and codecs (Release 6), December 2005. [MPEG2] ISO/IEC International Standard 13818-2:1993. [RFC2326] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998. [RFC2974] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. [RFC3450] Luby, M., Gemmell, J., Vicisano, L., Rizzo, L., and Crowcroft, J., "Asynchronous layered coding (ALC) protocol instantiation", RFC 3450, December 2002. [RFC3711] Baugher, M., McGrew, D, Naslund, M., Carrara, E., and Norrman, K., "The secure real-time transport protocol (SRTP)", RFC 3711, March 2004. [Yan] Yan, J., Katrinis, K., May, M., and Plattner, R., "Media- And TCP-friendly congestion control for scalable video streams", in IEEE Trans. Multimedia, pages 196--206, April 2006. 15. Author's Addresses Wenger, Wang, Schierl Expires June 17, 2008 [Page 57] Internet-Draft RTP Payload Format for SVC Video December 2007 Stephan Wenger Nokia 955 Page Mill Road Palo Alto, CA 94304 USA Phone: +1-650-862-7368 Email: stewe@stewe.org Ye-Kui Wang Nokia Research Center P.O. Box 100 FIN-33721 Tampere Finland Phone: +358-50-486-7004 Email: ye-kui.wang@nokia.com Thomas Schierl Fraunhofer HHI Einsteinufer 37 D-10587 Berlin Germany Phone: +49-30-31002-227 Email: schierl@hhi.fhg.de 16. Copyright Statement Full Copyright Statement Copyright (C) The IETF Trust (2007). 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. 17. Disclaimer of Validity This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS 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. 18. Intellectual Property Statement Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights Wenger, Wang, Schierl Expires June 17, 2008 [Page 58] Internet-Draft RTP Payload Format for SVC Video December 2007 might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf-ipr@ietf.org. 19. Acknowledgement Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). 20. RFC Editor Considerations none 21. Open Issues 1. Cross layer decoding order dependency - two suggested solutions on the table. Need to agree if use one or both. In the case of both how to resolve interoperability. Initial step is to update text explaining the usage. 2. Backward compatibility to H264 enabling H264 (RFC 3984 single NAL unit) to interoperate with H.264SVC using base layer. Need more definition. 3. Clarify the PACSI packet since there were changes between the draft revision 4. Fix the format of the document and review the SDP parameters. 5. Changed semantics between RFC 3984 and svc like sprop-deint-buf- req - probably will need new parameters. 6. What to do with bugs in RFC 3984 7. Clarify the usage of the new parameters like sprop-scalability- info, relation to SEI and usage in offer/answer 8. The text should be clear enough to allow an implementer to use it for creating the payload without having to read the H.264 SVC document. 22. Changes Log Version 00 Wenger, Wang, Schierl Expires June 17, 2008 [Page 59] Internet-Draft RTP Payload Format for SVC Video December 2007 - 29.08.2005, YkW: Initial version - 29.09.2005, Miska: Reviewed and commented throughout the document - 05.10.2006, StW: Editorial changes through the document, and formatted the document in RFC payload format style From -00 to -01 - 04.02.2006, StW: Added details to scope - 04.02.2006, StW: Added short subsection 6.1 "Design Principles" - 04.02.2006, StW: Added section 15, "Application Examples" - 06.02 - 03.03.2006, YkW: Various modifications throughout the document - 13.02.2006 - 03.03.2006 , ThS: Added definitions and additional information to section 3.3, 5.1, 7 and 8, parameters in section 9.1 and added section 14 for NAL unit re-ordering for layered multicast. Further modifications throughout the document From -01 to -02 - 06.03.2006, StW: Editorial improvements - 26.05.2006, YkW: Updated NAL unit header syntax and semantics according to the latest draft SVC spec - 20.06.2006, Miska/YkW: Added section 6.10 "Payload Content Scalability Information (PACSI) NAL Unit" - 20.06.2006, YkW: Updated the NAL unit reordering process for layered multicast (removed the old section 14 "Informative Appendix: NAL Unit Re-ordering for Layered Multicast" and added the new section 13 "NAL Unit Reordering for Layered Multicast") From -02 to -03 - 05.09.2006, YkW: Updated the NAL unit header syntax, definitions, etc., according to the foreseen July JVT output. Updated possible MANE adaptation operations according to SPID, TL, DID and QL. Clarified the removal of single NAL unit packetiztaion mode. Added the support of SSRC multiplexing in layered multicast. - 08.09.2006, StW: Editorial changes throughout the document - 08.09.2006, YkW: Added the packetization rule for suffix NAL unit. - 19.09.2006, YkW: Moved/updated SSRC multiplexing support to section 6.2 ``RTP header usage''. Moved/updated the cross layer DON constraint to Section 6.6 ``Decoding order number''. Moved/updated the packetization rule when a SVC bistream is transported over more than one RTP session to Section 7 ``Packetization rules''. Removed Section 13 "Support of layered multicast". - 16.10, TS: Added detailed four-byte NAL unit header description. Change "AVC" to "H.264" conforming to 3984. Modifications throughout the document. Extended description of 3rd byte of PACSI NAL unit. Corrected terms RTP session and RTP packet stream in case of SSRC multiplexing. Added terms in definition section on RTP multiplexing. Constraints on optional media type parameters of 3984 for cross-layer DON (DON section and media type parameters). Copied parts of SI paper Wenger, Wang, Schierl Expires June 17, 2008 [Page 60] Internet-Draft RTP Payload Format for SVC Video December 2007 regarding mixer, translator and SSRC mux with SRTP to section application examples. Added section on SDP usage with Session and SSRC multiplexing. Added points in Design principles on translator/mixer and RTP multiplexing. Added additional founding information in Ack- section. Corrected reference for SVC and added reference for generic signaling. 17.10, StW: Fixed many editorials, clarified MANE, mixer, translator and RTP packet stream throughout doc (hopefully consistently) 18.10., removed comments, clarified B-Bit, changed definition of base- layer (do not need to be of the lowest temporal resolution), From -03 to draft-ietf-avt-rtp-svc-00 23.11.06, StW: Editorials throughout the memo 23.11.06, StW: removed all occurrences of the security discussions, as they are incorrect. When using SRTP, the RTCP is authenticated, implying that a translator cannot rewrite RTCP RRs, implying that RRs would be incorrect as soon as the session is modified (i.e. packets are being removed), implying that SSRC-mux does not work in multicast. 23.11.06, StW: rewrote congestion control 23.11.06, StW: removed application scenario related to SRTP, as this does not work (see above 23.11.06, StW: added informative reference to H.241 27/29.11.06, YkW: editorial changes throughout the document 27/29.11.06, YkW: alignment with the SVC specification 19.12.06, TS: TS: [SVC] is now the complete Joint Draft of H.264 TS: Removed SSRC Multiplexing TS: Changed use cases for MANE as a translator TS: Editorials throughout the document, alignment with SVC spec. 20-28.12.06, StW/TS/YkW: editorial changes throughout the document From draft-ietf-avt-rtp-svc-00 to draft-ietf-avt-rtp-svc-01 23.02.07, YkW/Miska Hannuksela: Added enhancements to PACSI NAL unit 01.03.07, Jonathan Lennox/YkW: Added recommendatory packetization rules for SEI messages and non-VCL NAL units 05.03.07, Thomas Wiegand/YkW: Added the fields of picture start, picture end, and Tl0PicIdx to PACSI NAL unit 05.03.07, TS: Draft conforms to new I-D style From draft-ietf-avt-rtp-svc-01 to draft-ietf-avt-rtp-svc-02 25-June-2007: TS Clarified definitions Layer, Operation Points, Removed FGS Aligned with JVT-W201 spec Use of DON in de-packetization Congestion control 25-June-2007: YkW Edit throughout the spec, aligned with JVT-X201 SVC spec Wenger, Wang, Schierl Expires June 17, 2008 [Page 61] Internet-Draft RTP Payload Format for SVC Video December 2007 09-July-2007: TS Further modifications and alignments with JVT-X201. 05-Dec-2007: TS Formatting corrected, ref to signaling draft corrected From draft-ietf-avt-rtp-svc-02 to draft-ietf-avt-rtp-svc-03 - 21-Aug-2007 to 24-Sep-2007: YkW 1) Resolved most of the comments sent to the AVT reflector and to the editors 2) Updated the intro text for parameter sets 3) Reordered the definitions according to alphabetical order and added some definitions 4) Added the NAL unit order recovery process for layered multicast using CL-DON in the PACSI NAL unit, thus to allow for layered multicast without requiring the non-interleaved packetization mode. The detailed NAL unit order recovery process added to section 8. 5) Added some packetization rules. Some of these were to resolve the "single NAL unit mode deprecation" issue. 6) Added semantics of the media type parameters inherited from RFC 3984, and added a couple of new parameters for negotiation of operation point. 7) Other edits throughout the document. - 16 to 18 November 2007: TS 1) Added the NAL unit order recovery process for layered multicast without using CL-DON, thus to allow for layered multicast without requiring the non-interleaved packetization mode. 2) Added the usages of the media type parameters, including SDP usage with offer/answer model, declarative usage, and examples. - 08 to 19 November 2007: YkW 1) Aligned the spec with the final version of the SVC spec. 2) Updated the congestion control part according to Colin Perkins' comment. 3) Checked the parameter set considerations and confirmed that the text in RFC 3984 is OK. 4) Updated the security considerations part. 5) Added justifications for some fields in the PACSI NAL units. From draft-ietf-avt-rtp-svc-03 to draft-ietf-avt-rtp-svc-04 - 18 December 2007: TS 1) Updated formatting in the Media Type Registration section 2) Updated the semantics of sprop-layer-range 3) Updated Open issues according to Roni's email 4) Corrected usage of "depend" in SDP example Wenger, Wang, Schierl Expires June 17, 2008 [Page 62]