Audio/Video Transport WG T. Kristensen Internet-Draft TANDBERG Intended status: Standards Track March 9, 2009 Expires: September 10, 2009 RTP Payload Format for H.264 RCDO Video draft-ietf-avt-rtp-h264-rcdo-02 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 September 10, 2009. 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 memo describes an RTP Payload format for the Reduced-Complexity Decoding Operation (RCDO) for H.264 Baseline profile bitstreams, as specified in H.241. RCDO reduces the decoding cost and resource Kristensen Expires September 10, 2009 [Page 1] Internet-Draft H.264 RCDO RTP Payload March 2009 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 4.1. RTP Header Usage . . . . . . . . . . . . . . . . . . . . . 4 4.2. Payload Header . . . . . . . . . . . . . . . . . . . . . . 4 5. Payload Examples . . . . . . . . . . . . . . . . . . . . . . . 4 6. Congestion Control Considerations . . . . . . . . . . . . . . . 4 7. Payload Format Parameters . . . . . . . . . . . . . . . . . . . 4 7.1. Media Type Definition . . . . . . . . . . . . . . . . . . . 4 8. Mapping to SDP . . . . . . . . . . . . . . . . . . . . . . . . 6 8.1. Offer/Answer Considerations . . . . . . . . . . . . . . . . 6 8.2. Declarative SDP Considerations . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7 10. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 7 12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 8 12.1. Normative References . . . . . . . . . . . . . . . . . . . 8 12.2. Informative references . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 9 Kristensen Expires September 10, 2009 [Page 2] Internet-Draft H.264 RCDO RTP Payload March 2009 1. Introduction The Reduced-Complexity Decoding Operation (RCDO) for H.264 offers a solution to support higher resolutions at the same high framerates used in current implementations, but with reduced processing requirements, compared to today's needs. This is achieved by reducing the complexity and thus the decoding cost/resource consumption of the video processing. ITU-T H.264 [4] and ITU-T H.241 [5], its associated video procedures and signalling recommendation, continue to evolve. The IETF RTP payload formats and parameters need to be updated to include important new functionalities not covered in RFC 3984 [3]. The RCDO approach is already addressed in the latest version of H.241 [5]. This proposal defines media type parameters, a new H.264 media subtype for RCDO and allows use in SDP. 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]. 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 is referred to several times in this memo. In order to signal H.264 additional modes the parameter AdditionalModesSupported is specified in Table 9f of H.241 [5]. Currently, the only mode defined is RCDO. Informational note: Other additional modes may be defined in the future. However, as H.264 additional modes may or may not be distinct from the Profiles in H.264 - these modes would require separate extensions to RFC 3984 [3]. To maintain backward compatibility with existing H.264 implementations, this memo proposes a separate media subtype for RCDO Kristensen Expires September 10, 2009 [Page 3] Internet-Draft H.264 RCDO RTP Payload March 2009 named H264-RCDO. 4. Payload Format Section 5 of RFC 3984 [3] applies. 4.1. RTP Header Usage Editorial note: Refer to RFC 3984 or include verbatim/sligthly modified version from Section 5 of RFC 3984 [3] in final version. 4.2. Payload Header Editorial note: Refer to RFC 3984 or include verbatim/sligthly modified version from Section 5 of RFC 3984 [3] in final version. 5. Payload Examples TBD or refer to RFC3984. 6. 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]. An additional requirement if best-effort service is being used is: users of this payload format MUST monitor packet loss to ensure that the packet loss rate is within acceptable parameters. 7. 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 [9]. 7.1. Media Type Definition Editorial note: For now we describe the changes and differences to the H264 media type. Copy unchanged parts verbatim from RFC 3984 in the final version and for IANA registration. The media subtype for the ITU-T H.264 | ISO/IEC 14496-10 codec is allocated from the IETF tree. The receiver MUST ignore any unspecified parameter. Kristensen Expires September 10, 2009 [Page 4] Internet-Draft H.264 RCDO RTP Payload March 2009 Type name: video Subtype name: H264-RCDO Required parameters: rate: Indicates the RTP timestamp clock rate. The rate value MUST be 90000. Optional parameters: The optional media type parameters specified in RFC 3984 [3] apply, with the following constraints: profile-level-id: 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. 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. Encoding considerations: This type is only defined for transfer via RTP (RFC 3550). Security considerations: See section X of RFC YYYY. (TBD. Update when this memo becomes an RFC) Interoperability considerations: None Published specification: (TBD. Update when this memo becomes an RFC. Also refer to H.264 and H.241 in an IANA way.) Applications that use this media type: None Kristensen Expires September 10, 2009 [Page 5] Internet-Draft H.264 RCDO RTP Payload March 2009 Additional information: None Magic number(s): None File extension(s): None Macintosh file type code(s): None 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. 8. 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 8.1. 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 H264-RCDO profile-level-id parameter can only take the value 0 (no profile) for the profile part. 8.2. Declarative SDP Considerations When H264-RCDO over RTP is offered with SDP in a declarative style, as in RTSP [13] or SAP [14], the considerations in Section 8.2.3 of Kristensen Expires September 10, 2009 [Page 6] Internet-Draft H.264 RCDO RTP Payload March 2009 RFC 3984 [3] apply. Note that the H264-RCDO profile-level-id parameter can only take the value 0 (no profile) for the profile part. 9. IANA Considerations This memo requests that IANA registers H264-RCDO as specified in Section Section 7.1. 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). 10. 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 memo 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 memo 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 [10] is recommended. Other mechanism that may be used are IPsec [11] and TLS [12] (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. 11. Acknowledgements The RTP Payload Formats HOWTO [15] was used for guidance and proved helpful in the process. 12. References Kristensen Expires September 10, 2009 [Page 7] Internet-Draft H.264 RCDO RTP Payload March 2009 12.1. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [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. 12.2. Informative references [9] Freed, N. and J. Klensin, "Media Type Specifications and Registration Procedures", BCP 13, RFC 4288, December 2005. [10] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K. Norrman, "The Secure Real-time Transport Protocol (SRTP)", RFC 3711, March 2004. [11] Kent, S. and K. Seo, "Security Architecture for the Internet Protocol", RFC 4301, December 2005. [12] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.1", RFC 4346, April 2006. [13] Schulzrinne, H., Rao, A., and R. Lanphier, "Real Time Streaming Protocol (RTSP)", RFC 2326, April 1998. Kristensen Expires September 10, 2009 [Page 8] Internet-Draft H.264 RCDO RTP Payload March 2009 [14] Handley, M., Perkins, C., and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. [15] Westerlund, M., "How to Write an RTP Payload Format", draft-ietf-avt-rtp-howto-06 (work in progress), March 2009. Author's Address 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 Kristensen Expires September 10, 2009 [Page 9]