draft-ietf-rtcweb-video-03.txt   draft-ietf-rtcweb-video-04.txt 
Network Working Group A.B. Roach Network Working Group A.B. Roach
Internet-Draft Mozilla Internet-Draft Mozilla
Intended status: Standards Track November 25, 2014 Intended status: Standards Track February 13, 2015
Expires: May 29, 2015 Expires: August 17, 2015
WebRTC Video Processing and Codec Requirements WebRTC Video Processing and Codec Requirements
draft-ietf-rtcweb-video-03 draft-ietf-rtcweb-video-04
Abstract Abstract
This specification provides the requirements and considerations for This specification provides the requirements and considerations for
WebRTC applications to send and receive video across a network. It WebRTC applications to send and receive video across a network. It
specifies the video processing that is required, as well as video specifies the video processing that is required, as well as video
codecs and their parameters. codecs and their parameters.
Status of This Memo Status of This Memo
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Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on May 29, 2015. This Internet-Draft will expire on August 17, 2015.
Copyright Notice Copyright Notice
Copyright (c) 2014 IETF Trust and the persons identified as the Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
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publication of this document. Please review these documents publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as the Trust Legal Provisions and are provided without warranty as
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1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. Pre and Post Processing . . . . . . . . . . . . . . . . . . . 2 3. Pre and Post Processing . . . . . . . . . . . . . . . . . . . 2
3.1. Camera Source Video . . . . . . . . . . . . . . . . . . . 3 3.1. Camera Source Video . . . . . . . . . . . . . . . . . . . 3
3.2. Screen Source Video . . . . . . . . . . . . . . . . . . . 3 3.2. Screen Source Video . . . . . . . . . . . . . . . . . . . 3
4. Stream Orientation . . . . . . . . . . . . . . . . . . . . . 3 4. Stream Orientation . . . . . . . . . . . . . . . . . . . . . 3
5. Mandatory to Implement Video Codec . . . . . . . . . . . . . 4 5. Mandatory to Implement Video Codec . . . . . . . . . . . . . 4
6. Codec-Specific Considerations . . . . . . . . . . . . . . . . 5 6. Codec-Specific Considerations . . . . . . . . . . . . . . . . 5
6.1. VP8 . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6.1. VP8 . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.2. H.264 . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6.2. H.264 . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7 10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 8 10.2. Informative References . . . . . . . . . . . . . . . . . 9
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
One of the major functions of WebRTC endpoints is the ability to send One of the major functions of WebRTC endpoints is the ability to send
and receive interactive video. The video might come from a camera, a and receive interactive video. The video might come from a camera, a
screen recording, a stored file, or some other source. This screen recording, a stored file, or some other source. This
specification defines how the video is used and discusses special specification defines how the video is used and discusses special
considerations for processing the video. It also covers the video- considerations for processing the video. It also covers the video-
related algorithms WebRTC devices need to support. related algorithms WebRTC devices need to support.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119]. document are to be interpreted as described in [RFC2119].
3. Pre and Post Processing 3. Pre and Post Processing
This section provides guidance on pre- or post-processing of video This section provides guidance on pre- or post-processing of video
streams. streams.
Unless specified otherwise by the SDP or codec, the color space Unless specified otherwise by the SDP or codec, the color space
SHOULD be sRGB [SRGB]. SHOULD be sRGB [SRGB]. For clarity, this the color space indicated
by codepoint 1 from "ColourPrimaries" as defined in [IEC23001-8].
TODO: I'm just throwing this out there to see if a specific proposal, Unless specified otherwise by the SDP or codec, the video scan
even if wrong, might draw more comment than "TBD". If you don't like pattern for video codecs is Y'CbCr 4:2:0.
sRGB for this purpose, comment on the rtcweb@ietf.org mailing list.
It has been suggested that the MPEG "Coding independent media
description code points" specification [IEC23001-8] may have
applicability here.
3.1. Camera Source Video 3.1. Camera Source Video
This document imposes no normative requirements on camera capture; This document imposes no normative requirements on camera capture;
however, implementors are encouraged to take advantage of the however, implementors are encouraged to take advantage of the
following features, if feasible for their platform: following features, if feasible for their platform:
o Automatic focus, if applicable for the camera in use o Automatic focus, if applicable for the camera in use
o Automatic white balance o Automatic white balance
o Automatic light level control o Automatic light level control
o Dynamic frame rate for video capture based on actual encoding in
use (e.g., if encoding at 15 fps due to bandwidth constraints, low
light conditions, or application settings, the camera will ideally
capture at 15 fps rather than a higher rate).
3.2. Screen Source Video 3.2. Screen Source Video
If the video source is some portion of a computer screen (e.g., If the video source is some portion of a computer screen (e.g.,
desktop or application sharing), then the considerations in this desktop or application sharing), then the considerations in this
section also apply. section also apply.
Because screen-sourced video can change resolution (due to, e.g., Because screen-sourced video can change resolution (due to, e.g.,
window resizing and similar operations), WebRTC video recipients MUST window resizing and similar operations), WebRTC video recipients MUST
be prepared to handle mid-stream resolution changes in a way that be prepared to handle mid-stream resolution changes in a way that
preserves their utility. Precise handling (e.g., resizing the preserves their utility. Precise handling (e.g., resizing the
element a video is rendered in versus scaling down the received element a video is rendered in versus scaling down the received
stream; decisions around letter/pillarboxing) is left to the stream; decisions around letter/pillarboxing) is left to the
discretion of the application. discretion of the application.
Note that the default video scan format (Y'CbCr 4:2:0) is known to be
less than optimal for the representation of screen content produced
by most systems in use at the time of this document's publication,
which generally use RGB with at least 24 bits per sample. In the
future, it may be advisable to use video codecs optimized for screen
content for the representation of this type of content.
Additionally, attention is drawn to the requirements in Additionally, attention is drawn to the requirements in
[I-D.ietf-rtcweb-security-arch] section 5.2 and the considerations in [I-D.ietf-rtcweb-security-arch] section 5.2 and the considerations in
[I-D.ietf-rtcweb-security] section 4.1.1. [I-D.ietf-rtcweb-security] section 4.1.1.
4. Stream Orientation 4. Stream Orientation
In some circumstances - and notably those involving mobile devices - In some circumstances - and notably those involving mobile devices -
the orientation of the camera may not match the orientation used by the orientation of the camera may not match the orientation used by
the encoder. Of more importance, the orientation may change over the the encoder. Of more importance, the orientation may change over the
course of a call, requiring the receiver to change the orientation in course of a call, requiring the receiver to change the orientation in
which it renders the stream. which it renders the stream.
While the sender may elect to simply change the pre-encoding While the sender may elect to simply change the pre-encoding
orientation of frames, this may not be practical or efficient (in orientation of frames, this may not be practical or efficient (in
particular, in cases where the interface to the camera returns pre- particular, in cases where the interface to the camera returns pre-
compressed video frames). Note that the potential for this behavior compressed video frames). Note that the potential for this behavior
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signaled in the SDP, then such implementations MAY make use of the signaled in the SDP, then such implementations MAY make use of the
codec-specific mechanisms instead. codec-specific mechanisms instead.
5. Mandatory to Implement Video Codec 5. Mandatory to Implement Video Codec
For the definitions of "WebRTC Brower," "WebRTC Non-Browser", and For the definitions of "WebRTC Brower," "WebRTC Non-Browser", and
"WebRTC-Compatible Endpoint" as they are used in this section, please "WebRTC-Compatible Endpoint" as they are used in this section, please
refer to [I-D.ietf-rtcweb-overview]. refer to [I-D.ietf-rtcweb-overview].
WebRTC Browsers MUST implement the VP8 video codec as described in WebRTC Browsers MUST implement the VP8 video codec as described in
[RFC6386] and H.264 as described in [H264]. [RFC6386] and H.264 Constrained Baseline as described in [H264].
WebRTC Non-Browsers that support transmitting and/or receiving video WebRTC Non-Browsers that support transmitting and/or receiving video
MUST implement the VP8 video codec as described in [RFC6386] and MUST implement the VP8 video codec as described in [RFC6386] and
H.264 as described in [H264]. H.264 Constrained Baseline as described in [H264].
To promote the use of non-royalty bearing video codecs, To promote the use of non-royalty bearing video codecs,
participants in the RTCWEB working group, and any successor participants in the RTCWEB working group, and any successor
working groups in the IETF, intend to monitor the evolving working groups in the IETF, intend to monitor the evolving
licensing landscape as it pertains to the two mandatory-to- licensing landscape as it pertains to the two mandatory-to-
implement codecs. If compelling evidence arises that one of the implement codecs. If compelling evidence arises that one of the
codecs is available for use on a royalty-free basis, the working codecs is available for use on a royalty-free basis, the working
group plans to revisit the question of which codecs are required group plans to revisit the question of which codecs are required
for Non-Browsers, with the intention being that the royalty-free for Non-Browsers, with the intention being that the royalty-free
codec will remain mandatory to implement, and the other will codec will remain mandatory to implement, and the other will
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SDP allows for codec-independent indication of preferred video SDP allows for codec-independent indication of preferred video
resolutions using the mechanism described in [RFC6236]. If a resolutions using the mechanism described in [RFC6236]. If a
recipient of video indicates a receiving resolution, the sender recipient of video indicates a receiving resolution, the sender
SHOULD accommodate this resolution, as the receiver may not be SHOULD accommodate this resolution, as the receiver may not be
capable of handling higher resolutions. capable of handling higher resolutions.
Additionally, codecs may include codec-specific means of signaling Additionally, codecs may include codec-specific means of signaling
maximum receiver abilities with regards to resolution, frame rate, maximum receiver abilities with regards to resolution, frame rate,
and bitrate. and bitrate.
Unless otherwise signaled in SDP, recipients of video streams are Unless otherwise signaled in SDP, recipients of video streams MUST be
MUST be able to decode video at a rate of at least 20 fps at a able to decode video at a rate of at least 20 fps at a resolution of
resolution of at least 320x240. These values are selected based on at least 320x240. These values are selected based on the
the recommendations in [HSUP1]. recommendations in [HSUP1].
Encoders are encouraged to support encoding media with at least the Encoders are encouraged to support encoding media with at least the
same resolution and frame rates cited above. same resolution and frame rates cited above.
6.1. VP8 6.1. VP8
For the VP8 codec, defined in [RFC6386], endpoints MUST support the For the VP8 codec, defined in [RFC6386], endpoints MUST support the
payload formats defined in [I-D.ietf-payload-vp8]. In addition they payload formats defined in [I-D.ietf-payload-vp8].
MUST support the 'bilinear' and 'none' reconstruction filters.
TODO: There have been claims that VP8 already requires supporting
both filters; if true, these do not need to be reiterated here.
In addition to the [RFC6236] mechanism, VP8 encoders MUST limit the In addition to the [RFC6236] mechanism, VP8 encoders MUST limit the
streams they send to conform to the values indicated by receivers in streams they send to conform to the values indicated by receivers in
the corresponding max-fr and max-fs SDP attributes. the corresponding max-fr and max-fs SDP attributes.
6.2. H.264 6.2. H.264
For the [H264] codec, endpoints MUST support the payload formats For the [H264] codec, endpoints MUST support the payload formats
defined in [RFC6184]. In addition, they MUST support Constrained defined in [RFC6184]. In addition, they MUST support Constrained
Baseline Profile Level 1.2, and they SHOULD support H.264 Constrained Baseline Profile Level 1.2, and they SHOULD support H.264 Constrained
High Profile Level 1.3. High Profile Level 1.3.
Implementations of the H.264 codec have utilized a wide variety of Implementations of the H.264 codec have utilized a wide variety of
optional parameters. To improve interoperability the following optional parameters. To improve interoperability the following
parameter settings are specified: parameter settings are specified:
packetization-mode: Packetization-mode 1 MUST be supported. Other packetization-mode: Packetization-mode 1 MUST be supported. Other
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High Profile Level 1.3. High Profile Level 1.3.
Implementations of the H.264 codec have utilized a wide variety of Implementations of the H.264 codec have utilized a wide variety of
optional parameters. To improve interoperability the following optional parameters. To improve interoperability the following
parameter settings are specified: parameter settings are specified:
packetization-mode: Packetization-mode 1 MUST be supported. Other packetization-mode: Packetization-mode 1 MUST be supported. Other
modes MAY be negotiated and used. modes MAY be negotiated and used.
profile-level-id: Implementations MUST include this parameter within profile-level-id: Implementations MUST include this parameter within
SDP and SHOULD interpret it when receiving it. SDP and MUST interpret it when receiving it.
max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br: These par max-mbps, max-smbps, max-fs, max-cpb, max-dpb, and max-br: These
ameters allow the implementation to specify that they can support
certain features of H.264 at higher rates and values than those parameters allow the implementation to specify that they can
signalled by their level (set with profile-level-id). support certain features of H.264 at higher rates and values than
those signalled by their level (set with profile-level-id).
Implementations MAY include these parameters in their SDP, but Implementations MAY include these parameters in their SDP, but
SHOULD interpret them when receiving them, allowing them to send SHOULD interpret them when receiving them, allowing them to send
the highest quality of video possible. the highest quality of video possible.
sprop-parameter-sets: H.264 allows sequence and picture information sprop-parameter-sets: H.264 allows sequence and picture information
to be sent both in-band, and out-of-band. WebRTC implementations to be sent both in-band, and out-of-band. WebRTC implementations
MUST signal this information in-band; as a result, this parameter MUST signal this information in-band. This means that WebRTC
will not be present in SDP. implementations MUST NOT include this parameter in the SDP they
generate.
TODO: Do we need to require the handling of specific SEI messages? H.264 codecs MAY send and MUST support proper interpretation of SEI
One example that has been raised is freeze-frame messages. "filler payload" and "full frame freeze" messages. "Full frame
freeze" messages are used in video switching MCUs, to ensure a stable
decoded displayed picture while switching among various input
streams.
When the use of the video orientation (CVO) RTP header extension is
not signaled as part of the SDP, H.264 implementations MAY send and
SHOULD support proper interpretation of Display Orientation SEI
messages.
Implementations MAY send and act upon "User data registered by Rec.
ITU-T T.35" and "User data unregistered" messages. Even if they do
not act on them, implementations MUST be prepared to receive such
messages without any ill effects.
Unless otherwise signaled, implementations that use H.264 MUST encode
and decode pixels with a implied 1:1 (square) aspect ratio.
7. Security Considerations 7. Security Considerations
This specification does not introduce any new mechanisms or security This specification does not introduce any new mechanisms or security
concerns beyond what the other documents it references. In WebRTC, concerns beyond what the other documents it references. In WebRTC,
video is protected using DTLS/SRTP. A complete discussion of the video is protected using DTLS/SRTP. A complete discussion of the
security can be found in [I-D.ietf-rtcweb-security] and security can be found in [I-D.ietf-rtcweb-security] and
[I-D.ietf-rtcweb-security-arch]. Implementers should consider [I-D.ietf-rtcweb-security-arch]. Implementers should consider
whether the use of variable bit rate video codecs are appropriate for whether the use of variable bit rate video codecs are appropriate for
their application based on [RFC6562]. their application based on [RFC6562].
Implementors making use of H.264 are also advised to take careful
note of the "Security Considerations" section of [RFC6184], paying
special regard to the normative requirement pertaining to SEI
messages.
8. IANA Considerations 8. IANA Considerations
This document requires no actions from IANA. This document requires no actions from IANA.
9. Acknowledgements 9. Acknowledgements
The authors would like to thank Gaelle Martin-Cocher, Stephan Wenger, The author would like to thank Gaelle Martin-Cocher, Stephan Wenger,
and Bernard Aboba for their detailed feedback and assistance with and Bernard Aboba for their detailed feedback and assistance with
this document. Thanks to Cullen Jennings for providing text and this document. Thanks to Cullen Jennings for providing text and
review. This draft includes text from draft-cbran-rtcweb-codec. review. This draft includes text from draft-cbran-rtcweb-codec.
10. References 10. References
10.1. Normative References 10.1. Normative References
[H264] ITU-T Recommendation H.264, "Advanced video coding for [H264] ITU-T Recommendation H.264, "Advanced video coding for
generic audiovisual services", April 2013. generic audiovisual services (V9)", February 2014,
<http://www.itu.int/rec/T-REC-H.264-201304-I>.
[HSUP1] ITU-T Recommendation H.Sup1, "Application profile - Sign [HSUP1] ITU-T Recommendation H.Sup1, "Application profile - Sign
language and lip-reading real-time conversation using low language and lip-reading real-time conversation using low
bit rate video communication", May 1999. bit rate video communication", May 1999,
<http://www.itu.int/rec/T-REC-H.Sup1>.
[I-D.ietf-payload-vp8] [I-D.ietf-payload-vp8]
Westin, P., Lundin, H., Glover, M., Uberti, J., and F. Westin, P., Lundin, H., Glover, M., Uberti, J., and F.
Galligan, "RTP Payload Format for VP8 Video", draft-ietf- Galligan, "RTP Payload Format for VP8 Video", draft-ietf-
payload-vp8-11 (work in progress), February 2014. payload-vp8-11 (work in progress), February 2014.
[I-D.ietf-rtcweb-overview] [I-D.ietf-rtcweb-overview]
Alvestrand, H., "Overview: Real Time Protocols for Alvestrand, H., "Overview: Real Time Protocols for
Browser-based Applications", draft-ietf-rtcweb-overview-12 Browser-based Applications", draft-ietf-rtcweb-overview-12
(work in progress), October 2014. (work in progress), October 2014.
[IEC23001-8] [IEC23001-8]
ISO/IEC 23001-8:2013/DCOR1, "Coding independent media ISO/IEC 23001-8:2013/DCOR1, "Coding independent media
description code points", 2013. description code points", 2013, <http://standards.iso.org/
ittf/PubliclyAvailableStandards/
c062088_ISO_IEC_23001-8_2013.zip>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4175] Gharai, L. and C. Perkins, "RTP Payload Format for [RFC4175] Gharai, L. and C. Perkins, "RTP Payload Format for
Uncompressed Video", RFC 4175, September 2005. Uncompressed Video", RFC 4175, September 2005.
[RFC4421] Perkins, C., "RTP Payload Format for Uncompressed Video: [RFC4421] Perkins, C., "RTP Payload Format for Uncompressed Video:
Additional Colour Sampling Modes", RFC 4421, February Additional Colour Sampling Modes", RFC 4421, February
2006. 2006.
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[RFC6386] Bankoski, J., Koleszar, J., Quillio, L., Salonen, J., [RFC6386] Bankoski, J., Koleszar, J., Quillio, L., Salonen, J.,
Wilkins, P., and Y. Xu, "VP8 Data Format and Decoding Wilkins, P., and Y. Xu, "VP8 Data Format and Decoding
Guide", RFC 6386, November 2011. Guide", RFC 6386, November 2011.
[RFC6562] Perkins, C. and JM. Valin, "Guidelines for the Use of [RFC6562] Perkins, C. and JM. Valin, "Guidelines for the Use of
Variable Bit Rate Audio with Secure RTP", RFC 6562, March Variable Bit Rate Audio with Secure RTP", RFC 6562, March
2012. 2012.
[SRGB] IEC 61966-2-1, "Multimedia systems and equipment - Colour [SRGB] IEC 61966-2-1, "Multimedia systems and equipment - Colour
measurement and management - Part 2-1: Colour management - measurement and management - Part 2-1: Colour management -
Default RGB colour space - sRGB.", October 1999. Default RGB colour space - sRGB.", October 1999, <http://
www.colour.org/tc8-05/Docs/colorspace/61966-2-1.pdf>.
[TS26.114] [TS26.114]
3GPP TS 26.114 V12.7.0, "3rd Generation Partnership 3GPP TS 26.114 V12.8.0, "3rd Generation Partnership
Project; Technical Specification Group Services and System Project; Technical Specification Group Services and System
Aspects; IP Multimedia Subsystem (IMS); Multimedia Aspects; IP Multimedia Subsystem (IMS); Multimedia
Telephony; Media handling and interaction (Release 12)", Telephony; Media handling and interaction (Release 12)",
September 2014. December 2014, <http://www.3gpp.org/DynaReport/26114.htm>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-rtcweb-rtp-usage] [I-D.ietf-rtcweb-rtp-usage]
Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time Perkins, C., Westerlund, M., and J. Ott, "Web Real-Time
Communication (WebRTC): Media Transport and Use of RTP", Communication (WebRTC): Media Transport and Use of RTP",
draft-ietf-rtcweb-rtp-usage-06 (work in progress), draft-ietf-rtcweb-rtp-usage-06 (work in progress),
February 2013. February 2013.
[I-D.ietf-rtcweb-security-arch] [I-D.ietf-rtcweb-security-arch]
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