Internet DRAFT - draft-kristensen-payload-rtp-h241param
draft-kristensen-payload-rtp-h241param
Payload WG T. Kristensen
Internet-Draft M. Walters
Updates: 6184 (if approved) Cisco
Intended status: Standards Track October 15, 2012
Expires: April 18, 2013
Additional H.241 Parameter in the RTP Payload Format for H.264 Video
draft-kristensen-payload-rtp-h241param-00
Abstract
As systems increasingly are able to run video at 60 frames per
second, there is a need to signal desired frame rate to optimise
resolution choices and to avoid unnecessary resource or energy usage.
This document updates RFC6184 and defines a new optional parameter
addressing recent extensions currently supported in H.323 systems:
The signalling of the maximum frames per second that can be
efficiently received or that can be sent.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on April 18, 2013.
Copyright Notice
Copyright (c) 2012 IETF Trust and the persons identified as the
document authors. All rights reserved.
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include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction and Overview . . . . . . . . . . . . . . . . . . 3
1.1. New Parameter max-fps . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Payload Format Parameters . . . . . . . . . . . . . . . . . . 4
3.1. Media Type Registration . . . . . . . . . . . . . . . . . 4
4. SDP Parameters . . . . . . . . . . . . . . . . . . . . . . . . 5
4.1. Mapping of the optional parameter to SDP . . . . . . . . . 5
4.2. Usage with SDP offer/answer . . . . . . . . . . . . . . . 5
4.3. Usage in Declarative Session Descriptions . . . . . . . . 5
4.4. Examples . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Co-existence . . . . . . . . . . . . . . . . . . . . . . . . . 6
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . . 7
9.2. Informative references . . . . . . . . . . . . . . . . . . 7
Appendix A. Change History . . . . . . . . . . . . . . . . . . . 7
A.1. draft-kristensen-avt-rtp-h241param-02 to
draft-kristensen-payload-rtp-h241param-00 . . . . . . . . 7
A.2. draft-kristensen-avt-rtp-h241param-01 to -02 . . . . . . . 8
A.3. draft-kristensen-avt-rtp-h241param-00 to -01 . . . . . . . 8
Appendix B. Figures . . . . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction and Overview
The extended video procedures and control signals for H.300 series
terminals in ITU-T H.241 [ITU.H241.2006], associated with the ITU-T
H.264 [ITU.H264.2007] codec, continue to evolve. This document
describes a new parameter specified in H.241 - Amendment 2
[ITU.H241Amd2.2009] used to indicate the maximum picture rate that
can be efficiently received or the maximum picture rate that can be
sent. This proposal defines a media type parameter for maximum
picture rate signalling and allows use in SDP-based systems, as this
is not covered in [RFC6184].
Editorial note: This draft may be used to specify further, new
H.264 RTP payload format parameters if applicable and when new
parameters are defined.
1.1. New Parameter max-fps
The use of MaxMBPS amd MaxFS, either signalled implicitly via
supported level or as the optional parameters max-mbps and max-fs
[RFC6184], underspecify the video stream and can lead to wasted
bandwidth and processing resources, as well as unnecessary energy
consumption and, where applicable, shorter battery duration.
For example, a decoder signalling support for w1080p30 (243000 MBPS
and 8100 MB) implicitly allows the sending of w720p60 (216000 MBPS
and 3600 MB). Similarly, if a decoder signalled support for w720p30
(108000 MBPS and 3600 MB) the encoder could choose to send w480p60,
w448p60 or even wCIF at 120 frames per second. Graphs visualizing
these examples are included in Appendix B, where the existing
parameters are used, with the addition of max-fps to constrain the
allowed parameter range as preferred.
Editorial note: The graphs in Appendix B will most likely be
removed in later version, toghether with shortening of the
description in this section.
If the encoder chooses to send at a higher frame rate than preferred
by the receiver side, the decoder will normally discard the
additional frames after decoding them. The transmission of the extra
frames and the processing of frames to just discard them are wasteful
and the bandwidth and processing could be used more effectively.
The new parameter MaxFPS is introduced in H.241 - Amendment 2 to
remove this issue, by constraining the allowed parameter range for
systems supporting this extension. This draft proposes adding the
optional parameter max-fps for use in SDP-based signalling.
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The specification of max-fps in this draft will also ease the
gatewaying between H.323 and SIP systems by making the translation
straight-forward for this parameter as well.
It is worth emphasizing that systems that does not support and
understand the max-fps parameter are free to produce streams as
before, within the bounds specified by the existing parameters.
2. Terminology
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 [RFC2119].
In video formats based on NTSC, 30 frames per second and 60 frames
per second are used repeatedly. However, the actual values are 30/
1.001=29.97 and 60/1.001=59.94. Values derived from these fractional
values MUST be used in signalling descriptions.
3. Payload Format Parameters
The optional H264 media subtype parameter max-fps specified below
comes in addition to the list of optional H264 media subtype
parameters defined in Section 8.1 of [RFC6184].
3.1. Media Type Registration
New OPTIONAL parameter:
max-fps: The value of max-fps is an integer indicating the maximum
frame rate in units of hundredths of frames per second that can be
efficiently received. The signaled highest level is conveyed in
the value of the profile-level-id parameter or the max-recv-level
parameter. The max-fps parameter MAY be used to signal that the
receiver has a constraint in that it is not capable of decoding
video efficiently at the full frame rate that is implied by the
signaled highest level and, if present, one or more of the
parameters max-mbps, max-smbps or max-fs.
Notice that the value of max-fps is not necessarily the frame rate
at which the maximum frame size can be sent, it constitutes a
constraint on maximum frame rate for all resolutions.
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Informational note: The max-fps parameter is semantically
different from max-mbps, max-smbps, max-fs, max-cpb, max-dpb,
and max-br in that max-fps is used to signal a constraint,
lowering the maximum frame rate from what is implied by the
signaled MaxMBPS and MaxFS.
The encoder MUST use a frame rate equal to or less than this
value. In cases where the max-fps parameter is absent, or not
understood, the encoder is free to choose any frame rate according
to the highest signaled level and any signaled optional
parameters.
4. SDP Parameters
4.1. Mapping of the optional parameter to SDP
The optional parameter max-fps, when present, MUST be included in the
"a=fmtp" line of SDP. The parameters in the "a=fmtp" line are
expressed as a media type string, in the form of a semicolon
separated list of parameter=value pairs.
4.2. Usage with SDP offer/answer
When H.264 is offered over RTP using SDP in an offer/answer exchange
[RFC3264] for negotiation of unicast streams, the following
limitations and rules applies:
The interpretation of the optional parameter max-fps depends on the
direction attribute. When the direction attribute is sendonly, then
it indicates the maximum picture rate that shall be sent. When the
direction attribute is sendrecv or recvonly, the value of this
parameter indicates the maximum picture frame rate that the receiver
can efficiently handle. Any encoder that understands the parameter
semantics shall constrain the frame rate to rates up to that
specified. A receiver should have the ability to process video from
a sender that does not understand this parameter.
The profile-level-id parameter MUST be present in the same receiver
capability description that contains this parameter.
4.3. Usage in Declarative Session Descriptions
When H.264 over RTP is offered with SDP in a declarative style, the
max-fps parameter MUST NOT be used.
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4.4. Examples
Two simple examples of SDP descriptions with the max-fps parameter.
A NTSC-based system supporting maximum 30 frames per second could
offer:
m=video 49170 RTP/AVP 98
a=rtpmap:98 H264/90000
a=fmtp:98 profile-level-id=42A01E; max-fps=2997
A description for a system supporting a true 60 frames per second:
m=video 49170 RTP/AVP 99
a=rtpmap:99 H264/90000
a=fmtp:99 profile-level-id=42A01E; max-fps=6000
5. Co-existence
The "a=framerate" limitation, as specified in [RFC4566] allows a
global maximum frame rate to be specified for the video media, this
limit applies to all codecs in the video media section. In cases
where both "a=framerate" and codec specific limits are specified, the
maximum frame rate that can be used for a codec is the minimum of the
values specified globally and specifically for a codec.
6. IANA Considerations
This draft updates RFC6184 by adding a new optional parameter to the
H264 media subtype. The parameter is specified in Section Section 3
of this document.
7. Security Considerations
No separate considerations introduced in this document. Refer to
section 9 of [RFC6184].
8. Acknowledgements
The authors would like to acknowledge Mo Zanaty (mzanaty@cisco.com),
Roni Even (even.roni@huawei.com) and Stephen Botzko
(stephen.botzko@polycom.com) for helpful input and comments.
9. References
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9.1. Normative References
[ITU.H241.2006]
International Telecommunications Union, "Extended video
procedures and control signals for H.300-series
terminals", ITU-T Recommendation H.241, May 2006.
[ITU.H241Amd2.2009]
International Telecommunications Union, "Extended video
procedures and control signals for H.300-series
terminals", ITU-T Recommendation H.241 - Amendment 2,
December 2009.
[ITU.H264.2007]
International Telecommunications Union, "Advanced video
coding for generic audiovisual services", ITU-
T Recommendation H.264, November 2007.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3264] Rosenberg, J. and H. Schulzrinne, "An Offer/Answer Model
with Session Description Protocol (SDP)", RFC 3264,
June 2002.
[RFC6184] Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP
Payload Format for H.264 Video", RFC 6184, May 2011.
9.2. Informative references
[RFC4566] Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
Description Protocol", RFC 4566, July 2006.
Appendix A. Change History
A.1. draft-kristensen-avt-rtp-h241param-02 to
draft-kristensen-payload-rtp-h241param-00
1. Normative description of max-fps as tentatively concluded on AVT
WG mainling list earlier.
2. Shortened text based on previous discussion on AVT WG mailing
list.
3. Submitted to Payload WG; draft name changed.
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A.2. draft-kristensen-avt-rtp-h241param-01 to -02
1. Note; the media type registration text was added between -00 and
-01 - along the lines of sar-supported in [RFC6184].
2. Changed back to -00 normative language for max-fps media type
registration in Section 3.1, use MAY not SHOULD for an OPTIONAL
parameter!
A.3. draft-kristensen-avt-rtp-h241param-00 to -01
1. Tightened text describing "a=maxprate" and H.26x frame rate
signalling parameters, to get the real message clearer through.
2. Emphasized the optimization and energy consumption/battery
duration as reasons for specifying max-pfs.
3. Added graphs as an aid visualizing the effect of max-fps,
together with macroblock and frame size signalling
4. Clarified the 60/30 and 29.97/59.94 value usage in the document.
5. A better text regarding co-existence with "a=framerate" added.
6. Misc. editorial fixes and cleanup.
Appendix B. Figures
Graphical representation of the usage of the existing parameters for
signalling supported number of macroblocks per second (MaxMBPS) and
frame size (MaxFS), with addition of the proposed max-fps parameter
in an example scenario. Figure 1 assumes that an encoder can encode
at one of three resolutions wCIF, w720p and w1080p, and three
different frame rates 30, 60 and 120 frames per second (fps), but not
all combinations of these are possible.
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|
|
20 fps +
|
|
|
|
30 fps + * * *
|
|
|
|
60 fps + * *
|
|
120 fps + *
|
|
+----------+----------+----------+----------+----------+--
0 2000 4000 6000 8000 10000
MaxFS
Figure 1: Encoder capabilities
The decoder can then signal its capabilities. For example, if it can
decode 108000 macroblocks per second, then the encoder can choose any
combination of frame size and frame rate within the dotted area as
shown in Figure 2.
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|. . . . . . . . . . . . . . . . . .
|. . . . . . . . . . . . . . . . .
20 fps +. . . . . . . . . . . . . . . .
|. . . . . . . . . . . . . . .
|. . . . . . . . . . . . . .
|. . . . . . . . . . . . .
|. . . . . . . . . . . .
30 fps +. * . . . . . . .*. . *
|. . . . . . . . . .
|. . . . . . . . .
|. . . . . . . .
|. . . . . . .
60 fps +. * . . . . *
|. . . . .
|. . . .
120 fps +. * .
|. .
|.
+----------+----------+----------+----------+----------+--
0 2000 4000 6000 8000 10000
MaxFS
Figure 2: MaxMBPS indicated
If the decoder signals a maximum frame size (either explicitly as
max-fs or via the supported level), then this further constrains the
choice of the decoder as shown in Figure 3.
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|. . . . . . . . .
|. . . . . . . . .|
20 fps +. . . . . . . . .|
|. . . . . . . . .|
|. . . . . . . . .|
|. . . . . . . . .|
|. . . . . . . . .|
30 fps +. * . . . . . . .* *
|. . . . . . . . .|
|. . . . . . . . .|
|. . . . . . . . |
|. . . . . . . |
60 fps +. * . . . . *
|. . . . . |
|. . . . |
120 fps +. * . |
|. . |
|. |
+---------+----------+----------+----------+----------+--
0 2000 4000 6000 8000 10000
MaxFS
Figure 3: MaxMBPS and MaxFS indicated
The parameter max-fps is added as a horizontal limit in Figure 4
according to the decoder's preferences. This restricts the available
parameter space for the encoder.
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|. . . . . . . . .
|. . . . . . . . .|
20 fps +. . . . . . . . .|
|. . . . . . . . .|
|. . . . . . . . .|
|. . . . . . . . .|
30 fps +. * . . . . . . .* *
|. . . . . . . . .|
|. . . . . . . . .|
|. . . . . . . . |
|. . . . . . . |
60 fps +--*--------------*--------------------------------------
| |
| |
120 fps + * |
| |
| |
+---------+----------+----------+----------+----------+--
0 2000 4000 6000 8000 10000
MaxFS
Figure 4: Adding max-fps to further constrain
Authors' Addresses
Tom Kristensen
Cisco
Philip Pedersens vei 22
N-1366 Lysaker
Norway
Email: tomkrist@cisco.com, tomkri@ifi.uio.no
Malcolm Walters
Cisco
14 Waterside Drive
Langley, Slough
UK
Email: malcowal@cisco.com
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