One document matched: draft-ietf-avt-rtp-h264-params-01.txt
Differences from draft-ietf-avt-rtp-h264-params-00.txt
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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