AVT R. Even Internet-Draft Polycom Expires: April 7, 2004 P. Koskelainen Nokia October 8, 2003 SDP parameters for supporting H.263 and H.261 options draft-even-avt-h263-h261-options-00.txt Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 7, 2004. Copyright Notice Copyright (C) The Internet Society (2003). All Rights Reserved. Abstract This document defines the syntax and the semantics of SDP parameters needed to support features of H.261 and H.263 video codecs. This optional parameters enables the H.261 and H.263 codecs to specify their functionality enabling better video support. The document specify codec specific parameters that can be used with SIP, SAP or any similar protocol that uses SDP to signal support of those codecs. Even & Koskelainen Expires April 7, 2004 [Page 1] Internet-Draft H263/1 codecs October 2003 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. H.261 Codec Parameters . . . . . . . . . . . . . . . . . . . . . 3 3. H.263 Codec Parameters . . . . . . . . . . . . . . . . . . . . . 4 4. Usage of SDP H.261 and H.263 options with SIP . . . . . . . . . 6 5. Use of SDP H.263 and H.261 options with SAP . . . . . . . . . . 7 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 7 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Intellectual Property and Copyright Statements . . . . . . . . . 9 Even & Koskelainen Expires April 7, 2004 [Page 2] Internet-Draft H263/1 codecs October 2003 1. Introduction Internet multimedia conferencing is picking up with point-to-point and multipoint video conferencing implementations. The common video codecs that are used in video conferencing applications include H.261[3] and the basic H.263 with its two revisions from 1998 and 2000[4]. The current usage of H.261[3] and H.263[4] is limited since the current SDP MIME types defined in RFC3555 [6] are defining only part of the functionality needed. This document specifies the SDP syntax and the semantics for describing the optional H.261 and H.263 features. The syntax in this document uses the SDP "a=fmtp" attribute which is meant to carry codec specific parameters. These codec specific parameters can be used with SIP[1], SAP[2] or any similar protocol that uses SDP to signal support of those codecs. 2. H.261 Codec Parameters For further description of these H.261 parameters refer to the ITU H.261 document[3]. The fmtp parameters for H.261 are represented in the SDP attribute. a=fmtp:xx H261_option The xx is the RTP payload number, it can be a static or dynamic payload number. The recommendation is to use dynamic payload number. The syntax of H261_option is H261_option = *Size SP | *Annex SP Size = "QCIF" "=" "mpi | "CIF" "=" mpi mpi = 1*2DIGIT Annex = "D" The Size parameter specifies the picture size supported and at what frame rate. H.261 defines two resolution QCIF and CIF. mpi is an integer value (1..4) and it means the maximum picture frame rate is (29.97/mpi) frames/sec. The definition of the mpi is according to the video codec specification. Annex D specifies support for still image graphics according to H.261 annex D. Even & Koskelainen Expires April 7, 2004 [Page 3] Internet-Draft H263/1 codecs October 2003 3. H.263 Codec Parameters H.263 has three MIME types defined in RFC3555. The parameters in this section may be used with any of the H263 MIME types. When used with H.263-2000 MIME subtype name, the optional parameters profile and levels must not be used. For description of these H.263 parameters refer to the ITU H.263 document[4]. The fmtp parameters for H.263 are represented in the SDP attribute. a=fmtp:xx H263_option The xx is the RTP payload number, it can be a static or dynamic payload number. The recommendation is to use dynamic payload number. The syntax of H263_option is H263_option = *Size SP | *Annex SP | *Params Size = "SQCIF" "=" "mpi | "QCIF" "=" mpi | "CIF" "=" mpi | "CIF4" "=" mpi I "CIF16" "=" mpi | "XMAX" "=" xmax SP "YMAX" "=" ymax SP "MPI" "=" mpi mpi = 1*2DIGIT xmax=1*4DIGIT ymax=1*4DIGIT The Size parameter specifies the picture size supported and at what frame rate. H.263 defines fixed resolution SQCIF, QCIF, CIF, 4xCIF and 16xCIF as well as custom picture size that are presented by their maximum X and Y size. The X and Y values must be dividable by 4. mpi is an integer value (1..32) and it means the maximum picture frame rate is (29.97/mpi) frames/sec. The definition of the mpi is according to the video codec specification. Annex = "D" "=" #annex_d | "E" | "F" | "G" | "I" | "J" | "K" "=" #annex_k | "L" "=" #annex_l | "M" | "N" "=" annex_n | "O" "=" #annex_o | "P" | "Q" | "R" | "S" | "T" annex_d= "1" | "2" Even & Koskelainen Expires April 7, 2004 [Page 4] Internet-Draft H263/1 codecs October 2003 annex_k= "1" | "2" | "3" | "4" annex_l= "1" | "2" | "3" | "4" | "5" | "6" | "7" annex_n= "1" | "2" | "3" | "4" annex_o= "1" | "2" | "3" Here #term means comma separated list of term. The H.263 parameters that can be specified are in the Params options. Params= "PAR" "=" par_a ":" par_b | "CPCF" "=" cpcf | "MaxBR" "=" maxbr | "BPP" "=" bpp | "HRD" | "Interlaced" par_a=1*3DIGIT par_b=1*DIGIT cpcf=1*2DIGIT "." 1*3DIGIT maxbr=1*5DIGIT bpp=1*5DIGIT Explanations: Arbitrary Pixel Aspect Ratio (PAR): Par_a and par_b are integers between 0 and 255. Default ratio is 12:11 if not otherwise specified. Arbitrary (Custom) Picture Clock Frequency (CPCF): Cpcf is floating point value. Default value is 29.97. MaxBitRate (MaxBR): Maximum video stream bitrate, presented with units of 100 bits/s. MaxBR value is an integer between 1..19200. BitsPerPictureMaxKb (BPP): Maximum amount of kilobits allowed to represent a single picture frame, value is specified by largest supported picture resolution, Even & Koskelainen Expires April 7, 2004 [Page 5] Internet-Draft H263/1 codecs October 2003 see [1]. If this parameter is not present, then default value, that is based on the maximum supported resolution, is used. BPP is integer value between 0 and 65536. Hypothetical Reference Decoder (HRD): See annex B of H.263 specification. Interlaced or 60 fields indicates the support for interlace display according to H.263 annex W.6.3.11 These parameters are separated by space. 4. Usage of SDP H.261 and H.263 options with SIP This document does not specify actual SIP signaling. The decoder send its preferred parameters and let the other end select according to SIP procedures. This syntax may be sent, for example, with SIP INVITE and corresponding status response (200 ok). Other SIP methods may be used. Codec options: (D,E,F,G,I,J,K,L,M,N,O,P,Q,R,S,T) These characters exist only if the sender of this SDP message is able or willing to decode those. E.g. If a terminal is capable of decoding Syntax based Arithmetic Coding (SAC) and Advanced Prediction (AP) options, it can put E F in the end of the format specific parameters. Picture sizes and MPI: Supported picture sizes and their corresponding minimum picture interval (MPI) information for H.261 and H.263 can be combined. All picture sizes can be advertised to other party, or only some subset of it. Terminal announces only those picture sizes (with their MPIs) which it is willing to receive. For example, MPI=2 means that maximum (decodeable) picture rate per second is about 15. Parameters occurring first are the most preferred picture mode to be received. Example of the usage of these parameters: CIF=4 QCIF=3 SQCIF=2 XMAX=360 YMAX=240 MPI=2 This means that sender hopes to receive CIF picture size, which it can decode at MPI=4. If that is not possible, then QCIF with MPI value 3, if that is neither possible, then SQCIF with MPI value =2. It is also allowed (but least preferred) to send arbitrary picture sizes (max 360x240) with MPI=2. Note that most encoders support at Even & Koskelainen Expires April 7, 2004 [Page 6] Internet-Draft H263/1 codecs October 2003 least QCIF and CIF fixed resolutions and they are expected to be available almost in every H.261 and H.263 based video application. MaxBR and BPP parameters: Both these parameters are useful in SIP. MaxBitRate is video decoder property, hence it differs from SDP b : bandwidth-value attribute which refers more to application's total bandwidth (an application consists often of both audio and video). BitsPerPictureMaxKb is needed especially for decoder buffer size estimation to reduce the probability of video buffer overflow. Below is an example of H.263 SDP syntax in SIP message. a=fmtp: xx CIF=4 QCIF=2 MaxBR=1000 E F This means that the sender of this message can decode H.263 bit stream with following options and parameters: Preferred resolution is CIF (its MPI is 4), but if that is not possible then QCIF size is ok. Maximum receivable bitrate is 100 kbit/s (1000*100 bit/s) and SAC and AP options can be used. 5. Use of SDP H.263 and H.261 options with SAP SAP announcements are one-way only. All H.263/H.261 options can be used to signal that the sending terminal is going to use these options in its transmitted video stream. It is just an informal message. Usually only one picture size (with its MPI) exists. However, since it is possible for a video source (terminal) to change its picture size during session, several picture sizes can exist in the parameter list. First one is the original picture size to be used in the beginning of the session. 6. Security Considerations The security for these features are the same as for SDP. References [1] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston, A., Peterson, J., Sparks, R., Handley, M. and E. Schooler, "SIP: Session Initiation Protocol", RFC 3261, June 2002. [2] Handley, M., Perkins, C. and E. Whelan, "Session Announcement Protocol", RFC 2974, October 2000. Even & Koskelainen Expires April 7, 2004 [Page 7] Internet-Draft H263/1 codecs October 2003 [3] International Telecommunications Union, "Video codec for audiovisual services at p x 64 kbit/s", ITU-T Recommendation H.261, March 1993. [4] International Telecommunications Union, "Video coding for low bit rate communication", ITU-T Recommendation H.263, February 1998. [5] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with Session Description Protocol (SDP)", RFC 3264, June 2002. [6] Casner, S. and P. Hoschka, "MIME Type Registration of RTP Payload Formats", RFC 3555, July 2003. Authors' Addresses Roni Even Polycom 94 Derech Em Hamoshavot Petach Tikva 49130 Israel EMail: roni.even@polycom.co.il Petri Koskelainen Nokia P.O. Box 100 (Visiokatu 1) Tampere FIN-33721 Finland EMail: petri.koskelainen@nokia.com Even & Koskelainen Expires April 7, 2004 [Page 8] Internet-Draft H263/1 codecs October 2003 Intellectual Property Statement The IETF takes no position regarding the validity or scope of any intellectual property 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; neither does it represent that it has made any effort to identify any such rights. Information on the IETF's procedures with respect to rights in standards-track and standards-related documentation can be found in BCP-11. 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