Audio/Video Transport WG T. Kristensen Internet-Draft P. Luthi Intended status: Standards Track TANDBERG Expires: April 5, 2010 October 2, 2009 RTP Payload Format for H.264 RCDO Video draft-ietf-avt-rtp-h264-rcdo-03 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and 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 April 5, 2010. Copyright Notice Copyright (c) 2009 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents in effect on the date of publication of this document (http://trustee.ietf.org/license-info). Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Abstract This document describes an RTP Payload format for the Reduced- Complexity Decoding Operation (RCDO) for H.264 Baseline profile bitstreams, as specified in ITU-T Recommendation H.241. RCDO reduces Kristensen & Luthi Expires April 5, 2010 [Page 1] Internet-Draft H.264 RCDO RTP Payload October 2009 the decoding cost and resource consumption of the video processing. The RTP Payload format is based on the description in RFC 3984. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Conventions, Definitions and Acronyms . . . . . . . . . . . . 3 3. Media Format Background . . . . . . . . . . . . . . . . . . . 3 4. Payload Format . . . . . . . . . . . . . . . . . . . . . . . . 4 5. Congestion Control Considerations . . . . . . . . . . . . . . 4 6. Payload Format Parameters . . . . . . . . . . . . . . . . . . 4 6.1. Media Type Definition . . . . . . . . . . . . . . . . . . 4 7. Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . . . 15 7.1. Offer/Answer Considerations . . . . . . . . . . . . . . . 15 7.2. Declarative SDP Considerations . . . . . . . . . . . . . . 15 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16 9. Security Considerations . . . . . . . . . . . . . . . . . . . 16 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16 11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 11.1. Normative References . . . . . . . . . . . . . . . . . . . 16 11.2. Informative references . . . . . . . . . . . . . . . . . . 17 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Kristensen & Luthi Expires April 5, 2010 [Page 2] Internet-Draft H.264 RCDO RTP Payload October 2009 1. Introduction ITU-T Recommendation H.241 [5] specifies a reduced-complexity decoding operation (RCDO) for use with H.264 [4] Baseline profile bitstreams. It also specifies a bitstream constraint associated with RCDO and a mechanism for signalling RCDO within the bitstream that the bitstream conforms to the bitstream constraint and that the decoder applies the RCDO decoding process to the bitstream. RCDO for H.264 offers a solution to support higher resolutions at the same high framerates used in current implementations. This is achieved by reducing the processing requirements and thus the decoding cost/resource consumption of the video processing. 2. Conventions, Definitions and Acronyms 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 [1]. RFC-editor note: RFC XXXX is to be replaced by the RFC number this specification recieves when published. 3. Media Format Background The Reduced-Complexity Decoding Operation (RCDO) for H.264 Baseline profile bitstreams is specified in Annex B of H.241 [5]. RCDO is specified as a separate H.264 mode, and is distinct from any profile defined in H.264. An RCDO bitstream obey to all the constraints of the Baseline profile. The media format is based on the H.264 RTP Payload format as specified in RFC 3984 [3]. Therefore, RFC 3984 constitutes the basis for this document and is referred to several times. In order to signal H.264 additional modes, Table 9f of H.241 [5] specifies an AdditionalModesSupported parameter. Currently, the only additional mode defined is RCDO. Informative note: Other additional modes may be defined in the future. H.264 additional modes may or may not be distinct from the Profiles in H.264. A separate media subtype, named H264-RCDO, is defined to ensure backward compatibility with deployed implementations of H.264. Kristensen & Luthi Expires April 5, 2010 [Page 3] Internet-Draft H.264 RCDO RTP Payload October 2009 4. Payload Format The payload format defined in Section 5 of RFC 3984 [3] SHALL be used. This includes the RTP header usage and the payload format in RFC 3984. Examples of typical RTP packets can be found in RFC 3984. 5. Congestion Control Considerations Congestion control for RTP SHALL be used in accordance with RFC 3550 [6], and with any applicable RTP profile; e.g., RFC 3551 [7]. If best-effort service is being used, users of this payload format SHALL monitor packet loss to ensure that the packet loss rate is within acceptable parameters. 6. Payload Format Parameters This RTP payload format is identified using the H264-RCDO media type which is registered in accordance with RFC 4855 [8] and using the template of RFC 4288 [10]. 6.1. Media Type Definition Informative note: The media type definition for H264-RCDO is based on the definition for the H264 media subtype as specified in Section 8.1 of RFC 3984 [3]. Except for the profile-level-id parameter where new semantics are specified below, the optional media type parameters are copied verbatim from RFC 3984 [3] for completeness in the IANA registration. The media subtype for RCDO for H.264 is allocated from the IETF tree. The receiver MUST ignore any unspecified parameter. Type name: video Subtype name: H264-RCDO Required parameters: rate: Indicates the RTP timestamp clock rate. The rate value MUST be 90000. Optional parameters: Kristensen & Luthi Expires April 5, 2010 [Page 4] Internet-Draft H.264 RCDO RTP Payload October 2009 profile-level-id: A base16 RFC 3548 [9] (hexadecimal) representation of the following three bytes in the sequence parameter set NAL unit specified in H.264 [4]: 1) profile_idc, 2) a byte herein referred to as profile-iop, composed of the values of constraint_set0_flag, constraint_set1_flag, constraint_set2_flag, and reserved_zero_5bits in bit-significance order, starting from the most significant bit, and 3) level_idc. RCDO is distinct from any profile, this implies that the profile value 0 (no profile) and the profile_idc byte of the profile- level-id parameter are equal to 0. An RCDO bitstream MUST obey to all the constraints of the Baseline profile. Therefore, only constraint_set0_flag is equal to 1 in the profile-iop part of the profile-level-id parameter, the remaining bits are set to 0. If the profile-level-id parameter is used to indicate properties of a NAL unit stream, it indicates the level that a decoder has to support in order to comply with H.264 [4] when it decodes the stream. If the profile-level-id parameter is used for capability exchange or session setup procedure, it indicates the highest level supported for the signaled profile. For example, if a codec supports level 2.1, the profile-level-id becomes 00800d, in which 00 indicates the "no profile" value, 80 indicates the constraints of the Baseline profile and 0d indicates level 1.3. When level 2.1 is supported, the profile-level-id becomes 008015. If no profile-level-id is present, level 1 MUST be implied, i.e. equivalent to profile-level-id 00800a. max-mbps, max-fs, max-cpb, max-dpb, and max-br: These parameters MAY be used to signal the capabilities of a receiver implementation. These parameters MUST NOT be used for any other purpose. The profile-level-id parameter MUST be present in the same receiver capability description that contains any of these parameters. The level conveyed in the value of the profile-level-id parameter MUST be such that the receiver is fully capable of supporting. max- mbps, max-fs, max-cpb, max- dpb, and max-br MAY be used to indicate capabilities of the receiver that extend the required capabilities of the signaled level, as specified below. 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 Kristensen & Luthi Expires April 5, 2010 [Page 5] Internet-Draft H.264 RCDO RTP Payload October 2009 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 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 MIME type parameters are used to signal the properties of a NAL unit stream, max-mbps, max-fs, max-cpb, max-dpb, and max-br are not present, and the value of profile- level-id must always be such that the NAL unit stream complies fully with the specified profile and level. max-mbps: The value of max-mbps is an integer indicating the maximum macroblock processing rate in units of macroblocks per second. The max-mbps parameter signals that the receiver is capable of decoding video at a higher rate than is required by the signaled level conveyed in the value of the profile-level-id parameter. When max-mbps is signaled, the receiver MUST be able to decode NAL unit streams that conform to the signaled level, with the exception that the MaxMBPS value in Table A-1 of H.264 [4] for the signaled level is replaced with the value of max-mbps. The value of max-mbps MUST be greater than or equal to the value of MaxMBPS for the level given in Table A-1 of H.264 [4]. 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 of H.264 [4] for the signaled level is replaced with the value of max-fs. The value of max-fs MUST be greater than or equal to the value of MaxFS for the level given in Table A-1 of H.264 [4]. Senders MAY use this knowledge to send larger pictures at a proportionally lower frame rate than is indicated in the signaled level. Kristensen & Luthi Expires April 5, 2010 [Page 6] Internet-Draft H.264 RCDO RTP Payload October 2009 max-cpb: The value of max-cpb is an integer indicating the maximum coded picture buffer size in units of 1000 bits for the VCL HRD parameters (see A.3.1 item i of H.264 [4]) and in units of 1200 bits for the NAL HRD parameters (see A.3.1 item j of H.264 [4]). The max-cpb parameter signals that the receiver has more memory than the minimum amount of coded picture buffer memory required by the signaled level conveyed in the value of the profile-level-id parameter. When max-cpb is signaled, the receiver MUST be able to decode NAL unit streams that conform to the signaled level, with the exception that the MaxCPB value in Table A-1 of H.264 [4] for the signaled level is replaced with the value of max-cpb. The value of max-cpb MUST be greater than or equal to the value of MaxCPB for the level given in Table A-1 of H.264 [4]. Senders MAY use this knowledge to construct coded video streams with greater variation of bit rate than can be achieved with the MaxCPB value in Table A-1 of H.264 [4]. Informative note: The coded picture buffer is used in the hypothetical reference decoder (Annex C) of H.264. The use of the hypothetical reference decoder is recommended in H.264 encoders to verify that the produced bitstream conforms to the standard and to control the output bitrate. Thus, the coded picture buffer is conceptually independent of any other potential buffers in the receiver, including de-interleaving and de-jitter buffers. The coded picture buffer need not be implemented in decoders as specified in Annex C of H.264, but rather standard- compliant decoders can have any buffering arrangements provided that they can decode standard-compliant bitstreams. Thus, in practice, the input buffer for video decoder can be integrated with de- interleaving and de-jitter buffers of the receiver. max-dpb: The value of max-dpb is an integer indicating the maximum decoded picture buffer size in units of 1024 bytes. The max-dpb parameter signals that the receiver has more memory than the minimum amount of decoded picture buffer memory required by the signaled level conveyed in the value of the profile-level-id parameter. When max-dpb is signaled, the receiver MUST be able to decode NAL unit streams that conform to the signaled level, with the exception that the MaxDPB value in Table A-1 of H.264 [4] 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: Kristensen & Luthi Expires April 5, 2010 [Page 7] Internet-Draft H.264 RCDO RTP Payload October 2009 Min(1024 * max-dpb / ( PicWidthInMbs * FrameHeightInMbs * 256 * ChromaFormatFactor ), 16) PicWidthInMbs, FrameHeightInMbs, and ChromaFormatFactor are defined in H.264 [4]. The value of max-dpb MUST be greater than or equal to the value of MaxDPB for the level given in Table A-1 of H.264 [4]. 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 and is a property of the video decoder only. There is no relationship between the size of the decoded picture buffer and the buffers used in RTP, especially de-interleaving and de-jitter buffers. max-br: The value of max-br is an integer indicating the maximum video bit rate in units of 1000 bits per second for the VCL HRD parameters (see A.3.1 item i of H.264 [4]) and in units of 1200 bits per second for the NAL HRD parameters (see A.3.1 item j of H.264 [4]). The max-br parameter signals that the video decoder of the receiver is capable of decoding video at a higher bit rate than is required by the signaled level conveyed in the value of the profile-level-id parameter. The value of max- br MUST be greater than or equal to the value of MaxBR for the level given in Table A-1 of H.264 [4]. 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 H.264 [4]). o When the max-cpb parameter is not present, the result of the following formula replaces the value of MaxCPB in Table A-1 of H.264 [4]: (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). Kristensen & Luthi Expires April 5, 2010 [Page 8] Internet-Draft H.264 RCDO RTP Payload October 2009 The value of max-br MUST be greater than or equal to the value MaxBR for the signaled level given in Table A-1 of H.264 [4]. Senders MAY use this knowledge to send higher bitrate video as allowed in the level definition of Annex A of H.264, to achieve improved video quality. Informative note: This parameter was added primarily to complement a similar codepoint in the ITU-T Recommendation H.245, so as to facilitate signaling gateway designs. No assumption can be made from the value of this parameter that the network is capable of handling such bit rates at any given time. In particular, no conclusion can be drawn that the signaled bit rate is possible under congestion control constraints. redundant-pic-cap: This parameter signals the capabilities of a receiver implementation. When equal to 0, the parameter indicates that the receiver makes no attempt to use redundant coded pictures to correct incorrectly decoded primary coded pictures. When equal to 0, the receiver is not capable of using redundant slices; therefore, a sender SHOULD avoid sending redundant slices to save bandwidth. When equal to 1, the receiver is capable of decoding any such redundant slice that covers a corrupted area in a primary decoded picture (at least partly), and therefore a sender MAY send redundant slices. When the parameter is not present, then a value of 0 MUST be used for redundant-pic-cap. When present, the value of redundant-pic-cap MUST be either 0 or 1. When the profile-level-id parameter is present in the same capability signaling as the redundant-pic-cap parameter, and 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. Kristensen & Luthi Expires April 5, 2010 [Page 9] Internet-Draft H.264 RCDO RTP Payload October 2009 sprop-parameter-sets: This parameter MAY be used to convey any sequence and picture parameter set NAL units (herein referred to as the initial parameter set NAL units) that MUST precede any other NAL units in decoding order. The parameter MUST NOT be used to indicate codec capability in any capability exchange procedure. The value of the parameter is the base64 RFC 3548 [9] representation of the initial parameter set NAL units as specified in sections 7.3.2.1 and 7.3.2.2 of H.264 [4]. 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 MIME 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 [5] (see section 12.1). When the value of packetization-mode is equal to 1, the non- interleaved mode, as defined in section 6.3 of RFC 3984, MUST be used. When the value of packetization-mode is equal to 2, the interleaved mode, as defined in section 6.4 of RFC 3984, MUST be used. The value of packetization mode MUST be an integer in the Kristensen & Luthi Expires April 5, 2010 [Page 10] Internet-Draft H.264 RCDO RTP Payload October 2009 range of 0 to 2, inclusive. sprop-interleaving-depth: This parameter MUST NOT be present when packetization-mode is not present or the value of packetization- mode is equal to 0 or 1. This parameter MUST be present when the value of packetization-mode is equal to 2. This parameter signals the properties of 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. The value of sprop-interleaving-depth MUST be an integer in the range of 0 to 32767, inclusive. sprop-deint-buf-req: This parameter MUST NOT be present when packetization-mode is not present or the value of packetization- mode is equal to 0 or 1. It MUST be present when the value of packetization-mode is equal to 2. sprop-deint-buf-req signals the required size of the deinterleaving buffer for the NAL unit stream. The value of the parameter MUST be greater than or equal to the maximum buffer occupancy (in units of bytes) required in such a deinterleaving buffer that is specified in section 7.2 of RFC 3984. It is guaranteed that receivers can perform the deinterleaving of interleaved NAL units into NAL unit decoding order, when the deinterleaving buffer size is at least the value of sprop-deint- buf-req in terms of bytes. The value of sprop-deint-buf-req MUST be an integer in the range of 0 to 4294967295, inclusive. Informative note: sprop-deint-buf-req indicates the required size of the deinterleaving buffer only. When network jitter can occur, an appropriately sized jitter buffer has to be provisioned for as well. deint-buf-cap: This parameter signals the capabilities of a receiver implementation and indicates the amount of deinterleaving buffer space in units of bytes that the receiver has available for reconstructing the NAL unit decoding order. A receiver is able to handle any stream for which the value of the sprop-deint-buf-req parameter is smaller than or equal to this parameter. Kristensen & Luthi Expires April 5, 2010 [Page 11] Internet-Draft H.264 RCDO RTP Payload October 2009 If the parameter is not present, then a value of 0 MUST be used for deint-buf-cap. The value of deint-buf-cap MUST be an integer in the range of 0 to 4294967295, inclusive. Informative note: deint-buf-cap indicates the maximum possible size of the deinterleaving buffer of the receiver only. When network jitter can occur, an appropriately sized jitter buffer has to be provisioned for as well. sprop-init-buf-time: This parameter MAY be used to signal the properties of a NAL unit stream. The parameter MUST NOT be present, if the value of packetization-mode is equal to 0 or 1. The parameter signals the initial buffering time that a receiver MUST buffer before starting decoding 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- buf-time MUST be an integer in the range of 0 to 4294967295, inclusive. Kristensen & Luthi Expires April 5, 2010 [Page 12] Internet-Draft H.264 RCDO RTP Payload October 2009 In addition to the signaled sprop-init-buf- time, receivers SHOULD take into account the transmission delay jitter buffering, including buffering for the delay jitter caused by mixers, translators, gateways, proxies, traffic-shapers, and other network elements. sprop-max-don-diff: This parameter MAY be used to signal the properties of a NAL unit stream. It MUST NOT be used to signal transmitter or receiver or codec capabilities. The parameter MUST NOT be present if the value of packetization-mode is equal to 0 or 1. sprop-max-don-diff is an integer in the range of 0 to 32767, inclusive. If sprop-max-don-diff is not present, the value of the parameter is unspecified. sprop-max- don-diff is calculated as follows: sprop-max-don-diff = max{AbsDON(i) - AbsDON(j)}, for any i and any j>i, where i and j indicate the index of the NAL unit in the transmission order and AbsDON denotes a decoding order number of the NAL unit that does not wrap around to 0 after 65535. In other words, AbsDON is calculated as follows: Let m and n be consecutive NAL units in transmission order. For the very first NAL unit in transmission order (whose index is 0), AbsDON(0) = DON(0). For other NAL units, AbsDON is calculated as follows: If DON(m) == DON(n), AbsDON(n) = AbsDON(m) If (DON(m) < DON(n) and DON(n) - DON(m) < 32768), AbsDON(n) = AbsDON(m) + DON(n) - DON(m) If (DON(m) > DON(n) and DON(m) - DON(n) >= 32768), AbsDON(n) = AbsDON(m) + 65536 - DON(m) + DON(n) If (DON(m) < DON(n) and DON(n) - DON(m) >= 32768), AbsDON(n) = AbsDON(m) - (DON(m) + 65536 - DON(n)) If (DON(m) > DON(n) and DON(m) - DON(n) < 32768), AbsDON(n) = AbsDON(m) - (DON(m) - DON(n)) where DON(i) is the decoding order number of the NAL unit having index i in the transmission order. The decoding order number is specified in section 5.5 of RFC 3984. Kristensen & Luthi Expires April 5, 2010 [Page 13] Internet-Draft H.264 RCDO RTP Payload October 2009 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 negative impact. Encoding considerations: This type is only defined for transfer via RTP (RFC 3550) and is framed and binary, see section 4.8 in RFC4288. Security considerations: See section X of RFC XXXX. Interoperability considerations: None Published specification: RFC XXXX and its reference section. Applications that use this media type: None Additional information: None Magic number(s): Kristensen & Luthi Expires April 5, 2010 [Page 14] Internet-Draft H.264 RCDO RTP Payload October 2009 File extension(s): Macintosh file type code(s): Person & email address to contact for further information: Tom Kristensen , Intended usage: COMMON Restrictions on usage: This media type depends on RTP framing, and hence is only defined for transfer via RTP, ref RFC3550. Transport within other framing protocols is not defined at this time. Author: Tom Kristensen Change controller: IETF Audio/Video Transport working group delegated from the IESG. 7. Mapping to SDP The mapping of the above defined payload format media type and its parameters SHALL be done according to Section 3 of RFC 4855 [8]. An example of media representation of a level 2 bitstream is as follows: m=video 54321 RTP/AVP 101 a=rtpmap:101 H264-RCDO/90000 a=fmtp:101 profile-level-id=008014;max-mbps=60000 7.1. Offer/Answer Considerations When H264-RCDO is offered over RTP using SDP in an Offer/Answer model [2] for unicast and multicast usage, the limitations and rules described in Section 8.2.2 of RFC 3984 [3] apply. Note that the profile_idc byte of the H264-RCDO profile-level-id parameter can only take the value of 0 (no profile). 7.2. Declarative SDP Considerations When H264-RCDO over RTP is offered with SDP in a declarative style, as in RTSP [14] or SAP [15], the considerations in Section 8.2.3 of RFC 3984 [3] apply. Note that the profile_idc byte of the H264-RCDO profile-level-id parameter can only take the value of 0 (no profile). Kristensen & Luthi Expires April 5, 2010 [Page 15] Internet-Draft H.264 RCDO RTP Payload October 2009 8. IANA Considerations This document requests that IANA registers H264-RCDO as specified in Section Section 6.1. The media type is also requested to be added to the IANA registry for "RTP Payload Format MIME types" (http://www.iana.org/assignments/rtp-parameters). 9. Security Considerations RTP packets using the payload format defined in this specification are subject to the security considerations discussed in the RTP specification [6], and in any applicable RTP profile. The main security considerations for the RTP packet carrying the RTP payload format defined within this document are confidentiality, integrity and source authenticity. Confidentiality is achieved by encryption of the RTP payload. Integrity of the RTP packets through suitable cryptographic integrity protection mechanism. Cryptographic system may also allow the authentication of the source of the payload. A suitable security mechanism for this RTP payload format should provide confidentiality, integrity protection and at least source authentication capable of determining if an RTP packet is from a member of the RTP session or not. Note that the appropriate mechanism to provide security to RTP and payloads following this document may vary. It is dependent on the application, the transport, and the signalling protocol employed. Therefore a single mechanism is not sufficient, although if suitable the usage of SRTP [11] is recommended. Other mechanism that may be used are IPsec [12] and TLS [13] (RTP over TCP), but also other alternatives may exist. Refer also to section 9 of RFC 3984 [3], as no reasons for separate considerations are introduced in this document. 10. Acknowledgements The authors would like to acknowledge Gisle Bjoentegaard for his technical contribution and review of the specification. 11. References 11.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Kristensen & Luthi Expires April 5, 2010 [Page 16] Internet-Draft H.264 RCDO RTP Payload October 2009 [2] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [3] Wenger, S., Hannuksela, M., Stockhammer, T., Westerlund, M., and D. Singer, "RTP Payload Format for H.264 Video", RFC 3984, February 2005. [4] International Telecommunications Union, "Advanced video coding for generic audiovisual services", ITU-T Recommendation H.264, March 2005. [5] International Telecommunications Union, "Extended video procedures and control signals for H.300-series terminals", ITU-T Recommendation H.241, May 2006. [6] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [7] Schulzrinne, H. and S. Casner, "RTP Profile for Audio and Video Conferences with Minimal Control", STD 65, RFC 3551, July 2003. [8] Casner, S., "Media Type Registration of RTP Payload Formats", RFC 4855, February 2007. [9] Josefsson, S., "The Base16, Base32, and Base64 Data Encodings", RFC 3548, July 2003. 11.2. Informative references [10] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [11] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. [12] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [13] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [14] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998. [15] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. Kristensen & Luthi Expires April 5, 2010 [Page 17] Internet-Draft H.264 RCDO RTP Payload October 2009 Authors' Addresses Tom Kristensen TANDBERG Philip Pedersens vei 22 N-1366 Lysaker Norway Phone: +47 67125125 Email: tom.kristensen@tandberg.com, tomkri@ifi.uio.no URI: http://www.tandberg.com Patrick Luthi TANDBERG Philip Pedersens vei 22 N-1366 Lysaker Norway Email: patrick.luthi@tandberg.com URI: http://www.tandberg.com Kristensen & Luthi Expires April 5, 2010 [Page 18]