Audio/Video Transport WG                              T. Kristensen, Ed.
Internet-Draft                                                  TANDBERG
Updates: 3984 (if approved)                                      R. Even
Intended status: Standards Track                                 Polycom
Expires: August 2, 2008                                 January 30, 2008


 Parameters for Static Macroblocks and Aspect Ratio in the RTP Payload
                         Format for H.264 Video
                   draft-ietf-avt-rtp-h264-params-01

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Copyright Notice

   Copyright (C) The IETF Trust (2008).

Abstract

   This document updates RFC 3984.  It defines new optional parameters
   addressing recent 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.




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Table of Contents

   1.  Introduction and Overview . . . . . . . . . . . . . . . . . . . 3
     1.1.  Static macroblocks  . . . . . . . . . . . . . . . . . . . . 3
     1.2.  Sample aspect ratio . . . . . . . . . . . . . . . . . . . . 3
   2.  Requirements notation . . . . . . . . . . . . . . . . . . . . . 4
   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
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . . . 7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9

































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1.  Introduction and Overview

   The ITU-T H.264 [4] codec and the extended video procedures and
   control signals for H.300 series terminals in ITU-T H.241 [5],
   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.

1.1.  Static macroblocks

   Running H.264 encode and decode operations require large amounts of
   video processing power.  The challenge being to sustain high frame
   rate (e.g. 30 frames/sec) with the large frame sizes 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
   resolution, a higher number of static macroblocks enables a
   correspondingly higher frame rate.  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].

1.2.  Sample aspect ratio

   Sample Aspect Ratio (SAR) is the intended ratio of the horizontal
   distance between the columns to the vertical distance between the
   rows of the luma sample array in a frame.  SAR 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 CIF picture with a 4:3 Picture Aspect Ratio
   (PAR) is 12:11.  For a CIF picture with a 16:9 PAR, the sample aspect
   ratio is 16:11.

   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



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   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 PAR such as 4:3 and 16:9.


2.  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].


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.









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      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/answer exchange
   [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



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   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 shall still display pictures encoded at other sample
   aspect ratios (though perhaps with geometric distortion).

   H.264 compliant encoders should choose to send a SAR which can be
   displayed without geometric distortion.  However, H.264 compliant
   encoders may choose to send pictures using any SAR.

   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
        Levels", BCP 14, RFC 2119, March 1997.

   [2]  Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model with



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        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.


Appendix A.  Change Log

   draft-kristensen-avt-rtp-h264-params-00:

   - 2007-06-19: Based on static macroblocks part of
   draft-kristensen-avt-rtp-h264-extension-00, restructured.  Added
   sample aspect ratio parameter from H.241.

   draft-ietf-avt-rtp-h264-params-00:

   - 2007-06-30: Editorial changes.  Input from G. Sullivan's review
   considered.

   - 2007-07-01: Better descriptions, tightened text.  Introduced the
   term PAR to explicitly distuingish it from SAR.

   draft-ietf-avt-rtp-h264-params-00 to -01:

   - 2007-07-03: Moved requirement/acronyms sections to after
   Introduction.

   - 2008-01-30: Mainly a keep-alive-submission.  Adding missing PAR for
   the first example with 12:11 SAR in Section 2.2.













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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






























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