Audio/Video Transport WG T. Kristensen, Ed. Internet-Draft TANDBERG Updates: 3984 (if approved) R. Even Intended status: Standards Track Polycom Expires: December 21, 2007 June 19, 2007 Parameters for Static Macroblocks and Aspect Ratio in the RTP Payload Format for H.264 Video draft-kristensen-avt-rtp-h264-params-00 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 December 21, 2007. Copyright Notice Copyright (C) The IETF Trust (2007). Abstract This document updates RFC 3984. It defines new optional parameters addressing new extensions currently supported in H.323 systems: The signalling of the maximum rate of static macroblocks a decoder is able to process. The signalling of the sample aspect ratio supported by the sender or the receiver. Kristensen & Even Expires December 21, 2007 [Page 1]
Internet-Draft New H.264 RTP parameters June 2007 Table of Contents 1. Requirements notation . . . . . . . . . . . . . . . . . . . . . 3 2. Introduction and Overview . . . . . . . . . . . . . . . . . . . 3 2.1. Static macroblocks . . . . . . . . . . . . . . . . . . . . 3 2.2. Sample aspect ratio . . . . . . . . . . . . . . . . . . . . 3 3. Payload Format Parameters . . . . . . . . . . . . . . . . . . . 4 3.1. Media Type Registration . . . . . . . . . . . . . . . . . . 4 4. SDP Parameters . . . . . . . . . . . . . . . . . . . . . . . . 5 4.1. Mapping of the optional parameters to SDP . . . . . . . . . 5 4.2. Usage with SDP offer/answer . . . . . . . . . . . . . . . . 5 4.3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 6 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 6 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 7. Normative References . . . . . . . . . . . . . . . . . . . . . 6 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7 Intellectual Property and Copyright Statements . . . . . . . . . . 8 Kristensen & Even Expires December 21, 2007 [Page 2]
Internet-Draft New H.264 RTP parameters June 2007 1. Requirements notation 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]. 2. Introduction and Overview ITU-T H.264 [4] codec and ITU-T H.241 [5], the extended video video procedures and control signals for H.300 series terminals, 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]. This document describes new parameters used to signal maximal number of static macroblocks per second and the sample aspect ratio of the H.264 video stream. The new parameters are already defined in the latest version of H.241 [5]. This proposal defines media type parameters for them and allows their use in SDP based systems. 2.1. Static macroblocks Running H.264 encode and decode operations require large amounts of video processing power. The challenge being to sustain high framerate (e.g. 30 frames/sec) with the large framesizes that stems from recent demand for HD resolution. In practice, a certain amount of macroblocks in the video stream, which do not change in a frame, can be defined as static and, this way, free up additional processing cycles for the handling of non-static macroblocks. Based on a given amount of video processing resources and a given framerate, a higher number of static macroblocks enables a correspondingly higher resolution. A new parameter MaxStaticMBPS (maximum static macroblocks per second) was introduced in H.241 to address this issue. The MaxStaticMBPS parameter is specified in Section 8.3.2.8 of H.241 [5]. 2.2. Sample aspect ratio Sample Aspect Ratio (SAR) is the ratio between the intended horizontal distance between the columns and the intended vertical distance between the rows of the luma sample array in a frame. Sample aspect ratio is expressed as h:v, where h is horizontal width and v is vertical height (in arbitrary units of spatial distance). A sample is an individual luma picture element ("pixel") making up the complete displayed image (including both fields in the case of interlaced-scan video). For example, the sample aspect ratio for a Kristensen & Even Expires December 21, 2007 [Page 3]
Internet-Draft New H.264 RTP parameters June 2007 CIF picture is 12:11. All systems which send H.264 video should indicate the sample aspect ratio in the VUI parameters specified in Annex E of H.264 [4]. In the absence of a H.264 VUI parameter aspect_ratio_idc value in the received H.264 bitstream, and in the case of an aspect_ratio_idc value equal to 0, the sample aspect ratio may be assumed to have a value according to Table 1b in H.241 [5]. This draft enables the receiver to indicate what sample aspect ratio it can support without distortion. This may help an encoder to support the different monitors being used today, which support different aspect ratios such as 4:3 and 16:9. 3. Payload Format Parameters The optional H264 media subtype parameters max-smbps, sar and esar specified below comes in addition to the list of optional H264 media subtype parameters defined in Section 8.1 of RFC 3984 [3]. 3.1. Media Type Registration New optional parameters: max-smbps: The value of max-smbps is an integer indicating the maximum static macroblock processing rate in units of static macroblocks per second, under the hypothetical assumption that all macroblocks are static macroblocks. When max-smbps is signalled the MaxMBPS value in Table A-1 of H.264 [4] should be replaced with the result of the following computation: 1. If the parameter max-mbps is signalled, set a variable MaxMacroblocksPerSecond to the value of max-mbps. Otherwise, set MaxMacroblocksPerSecond equal to the value of MaxMBPS for the level in Table A-1 of H.264 [4]. 2. Set a variable P_non-static to the proportion of non-static macroblocks in picture n. 3. Set a variable P_static to the proportion of static macroblocks in picture n. Kristensen & Even Expires December 21, 2007 [Page 4]
Internet-Draft New H.264 RTP parameters June 2007 4. The value of MaxMBPS in Table A-1 of H.264 [4] should be considered by the encoder to be equal to: 1 ----------------------------------------- P_non-static P_static ------------------------- + ----------- MaxMacroblocksPerSecond max-smbps The encoder should recompute this value for each picture. The value of max-smbps MUST be greater than 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 signalled level. sar: The value of this parameter is an integer that indicates support of sample aspect ratios corresponding to H.264 aspect_ratio_idc values in the range from 1 to N inclusive, where N is the value of this parameter (see Table E-1 of H.264 [4]). esar: The value of this parameter is 1 or 0. 1 indicates support for all sample aspect ratios which are expressible using the H.264 aspect_ratio_idc value of 255 (Extended_SAR, see Table E-1 of H.264 [4]). If the parameter does not exist, its value is 0. 4. SDP Parameters 4.1. Mapping of the optional parameters to SDP The optional parameters max-smbps, sar and esar 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 paremeter=value pairs. 4.2. Usage with SDP offer/answer When H.264 is offered over RTP using SDP in an Offer/Anwer model [2] for negotiation of unicast streams, the following limitations and rules applies: The optional parameter max-smbps is treated the same way as max-mbps, when used in both the SDP Offer/Answer model [2] and declarative session descriptions. Its 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 Kristensen & Even Expires December 21, 2007 [Page 5]
Internet-Draft New H.264 RTP parameters June 2007 attribute is sendrecv or recvonly, the parameters describe the limitations of what the receiver accepts. The profile-level-id parameter MUST be present in the same receiver capability description that contains this parameter. The interpretation of the optional parameter sar depends on the direction attribute. When the direction attribute is sendonly, then it indicates the range of sample aspect ratios the stream will contain. When the direction attribute is sendrecv or recvonly, the value of this parameter indicates the range of sample ratios that the receiver is able to display without geometric (shape) distortion. The receiver will still be able to display any other sample aspect ratio with distortion. H.264 compliant encoders may not be able to scale a picture, in this case the basic rule is that terminals which display received video shall be capable of displaying any picture format and frame rate for which they signal the capability. The format used to display such received video streams is not required to match the exact format transmitted. The optional parameter esar is a receiver capability that permits a terminal to signal additional abilities to display any decoded video expressible using the H.264 aspect_ratio_idc value of 255 (Extended_SAR, see Table E-1 of H.264 [4]). The actual extended aspect ratio is conveyed using H.264 VUI. 4.3. Examples TBD 5. IANA Considerations This draft updates RFC 3984 by adding three new optional parameters to the H264 media subtype. The parameters are specified in Section Section 3 of this document. 6. Security Considerations No separate considerations introduced in this document. Refer to section 9 of RFC 3984 [3]. 7. Normative References [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement Kristensen & Even Expires December 21, 2007 [Page 6]
Internet-Draft New H.264 RTP parameters June 2007 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. Authors' Addresses Tom Kristensen (editor) 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 Roni Even Polycom 94 Derech Em Hamoshavot Petach Tikva 49130 Israel Email: roni.even@polycom.co.il URI: http://www.polycom.com Kristensen & Even Expires December 21, 2007 [Page 7]
Internet-Draft New H.264 RTP parameters June 2007 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. 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. 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 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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Kristensen & Even Expires December 21, 2007 [Page 8]