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RTCWEB Working Group                                           B. Burman
Internet-Draft                                                  Ericsson
Intended status: Standards Track                              M. Isomaki
Expires: April 30, 2015                                            Nokia
                                                                B. Aboba
                                                   Microsoft Corporation
                                                        G. Martin-Cocher
                                                          BlackBerry Ltd
                                                              G. Mandyam
                                              Qualcomm Innovation Center
                                                               X. Marjou
                                                             C. Jennings
                                                            J. Rosenberg
                                                               D. Singer
                                                        October 27, 2014

         H.264 as Mandatory to Implement Video Codec for WebRTC


   This document proposes that, and motivates why, H.264 should be a
   Mandatory To Implement video codec for WebRTC.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on April 30, 2015.

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Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  H.264 Overview  . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  Implementations . . . . . . . . . . . . . . . . . . . . . . .   3
     4.1.  Software  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  Hardware  . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.3.  Standards . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  Deployment  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Licensing . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     6.1.  Royalty Free for Innovation, Low-volume Shipments . . . .   7
     6.2.  Higher H.264/AVC Profile Tools Bundled  . . . . . . . . .   8
     6.3.  Licensing Stability . . . . . . . . . . . . . . . . . . .   8
   7.  Performance . . . . . . . . . . . . . . . . . . . . . . . . .   9
   8.  Profile/level . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  Negotiation . . . . . . . . . . . . . . . . . . . . . . . . .  13
   10. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . .  14
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
   12. Security Considerations . . . . . . . . . . . . . . . . . . .  15
   13. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  15
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  15
     14.2.  Informative References . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19

1.  Introduction

   The selection of a Mandatory To Implement (MTI) video codec for
   WebRTC has been discussed for quite some time in the RTCWEB WG.  This
   document proposes that the H.264 video codec should be mandatory to
   implement for WebRTC implementations and gives motivation to this

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   The core of the proposal is that:

      H.264 Constrained Baseline Profile Level 1.2 MUST be supported as
      Mandatory To Implement video codec.

   To enable higher quality for devices capable of it:

      H.264 Constrained High Profile Level 1.3, logically extended to
      support 720p resolution at 30 Hz framerate is RECOMMENDED.

   This draft discusses the advantages of H.264 as the authors of this
   draft see them; a richness of implementations and hardware support,
   well known licensing conditions, good performance, and well defined
   handling of varying device capabilities.

2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in BCP 14, RFC 2119

3.  H.264 Overview

   The video coding standard Advanced Video Coding (ITU-T H.264 | ISO/
   IEC 14496-10 [H264]) has been around for almost ten years by now.
   Developed jointly by MPEG and ITU-T in the Joint Video Team, it was
   published in its first version in 2003 and amended with support for
   higher-fidelity video in 2004.  Other significant updates include
   support for scalability (2007) and multiview (2009).  The codec goes
   under the names H.264, AVC and MPEG-4 Part10.  In this memo the term
   "H.264" will be used.

   H.264 was from the start very successful and has become widely
   adopted for (video) content as well as (video) communication services

   H.264 is mandatory in mobile wireless standards for multimedia
   telephony and packet switched streaming.  It is also the leading de
   facto standard for web video content delivered in HTML5 or other
   technologies, and is supported in nearly all major web browsers,
   mobile device platforms, and desktop operating systems.

4.  Implementations

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4.1.  Software

   There are many software implementations of the H.264 standard,
   including royalty-free open source code from Cisco [OpenH264] and
   Polycom [Woon], both of which support H.264/SVC (Annex G).  Wikipedia
   provides an illustration of the long list of other available
   implementations [Implementations].

   The Cisco OpenH264 implementation is notable for also providing
   binaries for common platforms that can be downloaded directly to an
   end-user's device or application, so distribution royalties are paid
   by Cisco rather than the application developer.  The latest Mozilla
   Firefox browser release does just that - downloads an OpenH264 binary
   - making it possible to use H.264 in WebRTC sessions [FF33].

   Microsoft has also produced an H.264 prototype for use in browsers
   [CURtcWeb].  Not only are there standalone implementations available,
   including open source, but in addition recent Windows and Mac OS X
   versions support H.264 encoding and decoding.

4.2.  Hardware

   Arguably, hardware or DSP acceleration for video encoding/decoding
   would be mostly beneficial for devices that has relatively lower
   capacity in terms of CPU and power (smaller batteries), and the most
   common devices in this category are phones and tablets.  There is a
   long list of vendors offering hardware or DSP implementations of
   H.264.  In particular all vendors of platforms for mobile high-range
   phones, smartphones, and tablets support H.264/AVC High Profile
   encoding and decoding at least 1080p30, but those platforms are
   currently in general not used for low- to mid-range devices.  These
   vendors are Qualcomm, TI, Nvidia, Renesas, Mediatek, Huawei
   Hisilicon, Intel, Broadcom, Samsung.  Those platforms all support
   H.264/AVC codec with dedicated hardware or DSP.  The majority of the
   implementations also support low-delay real-time applications.

   The WebM wiki [WEBM] shows only 8 (out of ~68) SoCs which support VP8
   encode and decode.  This only represents a fraction of deployed SoCs.
   Almost all deployed SoCs, as well as future designs, support H.264
   encode and decode, including desktop (Intel x86) chipsets.

   The benefits of hardware encoder and decoder implementations
   typically have an order of magnitude or more performance advantage
   (e.g., 1080p versus 360p becomes achievable) and power savings (e.g.,
   tens of milliwatts versus many hundreds of milliwatts or even watts
   are consumed just by the encoder and decoder).  While VP8 proponents
   have argued codec power is not a major concern relative to displays,

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   this neglects the advances in display technology that put the central
   processor back near the top power consumers.

   The availability of hardware codecs for real-time communication to
   developers through public APIs is increasing.  As of iOS8, Apple has
   provided API for access to the hardware H.264 encoder and decoder on
   the iOS platforms.  The APIs can be found in the Video Toolbox
   [AppleVideoToolbox].  BlackBerry recently released the API
   [BlackBerryAPI] to the hardware H.264 codec via OpenMAX-AL [OpenMAX].
   Android has provided the MediaCodec API [MediaCodec] to the hardware
   H.264 codec since version 4.1 (API 16), as well as enhancements and a
   Compatibility Test Suite in 4.3 (API 18).

4.3.  Standards

   There are also other standards and specifications that support H.264.
   One notable area is wireless display standards, where H.264 support
   is pervasive among all the following leading standards:

   o  AirPlay (Apple) [AirPlay].

   o  WiDi (Intel) [WiDi].

   o  Miracast (Wi-Fi Alliance) [Miracast].

   o  Google Cast (Google) [GoogleCast].

   o  DLNA (Sony) [DLNA].

   GSMA [GSMA] has defined the following services for use in 3GPP
   [ThreeGPP] IP Multimedia Subsystem (IMS), which use H.264 Constrained
   Baseline Profile as MTI video codec:

   IR.94  IMS Profile for Conversational Video Service [IR94]

   IR.39  IMS Profile for High Definition Video Conference (HDVC)
      Service [IR39]

5.  Deployment

   Today, the Internet runs on H.264 for real-time video communications.
   Though not yet on the web, video communications is in widespread
   usage on the Internet.  It is supported in consumer applications both
   on the desktop and in mobile apps, provided by many players like
   Skype and Tango.  It is in widespread usage for business
   communications, in many applications like Webex, Citrix Go-To-
   Meeting, Tandberg and Polycom telepresence systems, and many more.

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   All of these are in widespread deployment and widespread usage, and
   are based on H.264.

   Today, every single GSM/WCDMA mobile device, mobile operator network
   and mobile operating system supports the H.264 Constrained Baseline
   Profile video codec [GSMA-Codec-WP].

   If we want WebRTC to be successful, we must make sure it is something
   that can be adopted by the application providers who deploy real-time
   communications on the Internet.  WebRTC needs to be for the
   developers - the people who are building applications.  And a
   critical target customer base are the ones who are already doing
   voice and video communications - the ones with the network effect and
   user bases which need to be tapped to make this technology
   successful.  If WebRTC does not embrace H.264, it will be at the risk
   of ignoring the needs of one of its most important set of potential
   adopters - the ones most eager to use it - the ones already in the
   market for real-time communications.

   It may be argued that clients can be upgraded to support any new
   codec.  Opus is mandatory despite no deployment.  However, G.711 is
   also mandatory to ensure broad adoption.  Likewise, H.264 should be
   mandatory to ensure broad video adoption, since it is as widely
   adopted in video as G.711 in voice.  Also, video is more processing
   intensive than voice, and therefore often implemented in hardware
   that is not easily upgradeable.  Other video systems use desktop
   software which can also be difficult to broadly upgrade.  Still
   others provide SDKs and toolkits to third parties which cannot easily
   be upgraded.  Others have mobile apps which users cannot be
   forcefully made to upgrade.

   It may be argued that clients must be upgraded anyway to support ICE,
   DTLS-SRTP and other WebRTC requirements.  Some will, some won't.  For
   the latter, application providers will need to build server side
   gateways.  While that adds cost and complexity, the need to transcode
   video would greatly escalate costs, perhaps making them prohibitive.
   The CPU cost for transcoding, and the corresponding impact on quality
   due to recoding and increased delays, are substantially larger
   compared to just transport-level gateway functions.  Perhaps enough
   to make it impractical at scale.  This view is supported by the
   discussion on transcoding in a GSMA whitepaper [GSMA-Codec-WP], where
   it is concluded that "...to preserve end-user experience, transcoding
   must be avoided altogether".

   It may be argued that deployed video systems and applications are
   insignificant compared to the larger number of web browsers that will
   support WebRTC.  This misses a key point.  Real-time communications
   exists amongst a set of users that can talk to each other, typically

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   because they are customers of the same service.  Skype users can talk
   to each other.  Tango users can talk to each other.  There is, to
   date, relatively little federation for video between these providers,
   a problem which WebRTC is unlikely to remedy, as its causes have
   little to do with media stacks, and everything to do with business.
   Enabling real-time communications in the browser does not immediately
   create a connected user base that is the size of the web.  WebRTC is
   just a media stack; the namespace is provided by the application
   provider, as is the size of the communications network to which that
   user can connect.  Existing communications providers greatly value
   their user bases, and those user bases define the reachable
   communications network.  When viewed in that lens, the most important
   thing for allowing a WebRTC user to reach a massive network, is
   enabling WebRTC to be usable by those which have existing networks of
   users.  Of those, many are asking for H.264.

   It may be argued that WebRTC should build for the future, and not be
   constrained by the past.  This is reminiscent of the arguments made
   by those who advocated against IETF doing work on NAT or making NAT
   friendly protocols.  The hope was the same - that IETF could, through
   standards, dictate the future as we wished it - that by designing
   protocols which didn't work through NAT, we would force the industry
   to move away from NAT and embrace IPv6.  That strategy failed.  The
   Internet is a living, breathing thing, constantly evolving.  Those
   technologies which are successful are actually those which work for
   the Internet as it is today, not the Internet as we wish it could be.
   Those then allow the Internet to take a baby step forward, and from
   there, another step forward.  Successful technologies require
   consideration for transition, as it is more important than the
   target.  Just like NAT was, and still is, a reality on the Internet
   today, so too is H.264 a reality of the Internet today.  Just like we
   could not upgrade the routers and switches to eliminate NAT, so too
   are we unable to upgrade many of the Internet endpoints today to
   instantly move away from H.264.  We should learn from the past and
   define a WebRTC which can work with the applications in existence
   today, otherwise we significantly hinder the success and growth of

6.  Licensing

6.1.  Royalty Free for Innovation, Low-volume Shipments

   MPEG-LA released their AVC Patent Portfolio License already in 2004
   and in 2010 they announced that H.264 encoded Internet video is free
   to end users will never be charged royalties [MPEGLA].  Real-time
   generated content, the content most applicable to WebRTC, was free
   already from the establishment of the MPEG-LA license
   [MPEGLA-License].  License fees for the distribution of products that

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   decode and encode H.264 video remain though.  Those fees
   [MPEGLA-Terms] are, and will very likely continue to be for the
   lifetime of MPEG-LA pool, $0.20 per codec or less.

   To paraphrase, the MPEG LA license does allow up to 100K units per
   year, per legal entity/company (type "a" sublicensees in MPEG LA's
   definition), to be shipped for zero ($0) royalty cost.  This should
   be adequate for many WebRTC innovators or start-ups to try out new
   implementations on a large set of users before incurring any patent
   royalty costs, a benefit to selecting a H.264/AVC profile as the
   mandatory codec.

6.2.  Higher H.264/AVC Profile Tools Bundled

   It should be noted that when one licenses the MPEG LA H.264/AVC pool,
   patents for higher profile tools - such as CABAC, 8x8 - are bundled
   in with those required for the Constrained Baseline Profile.  Thus,
   these could optionally be used by WebRTC implementers to achieve even
   greater performance or efficiencies than using H.264 Constrained
   Baseline Profile alone.

   It can also be noted that for MPEG-LA, since one license covers both
   an encoder and decoder, there is no additional cost of using an
   encoder to an implementation that supports decoding of H.264.

6.3.  Licensing Stability

   H.264 is a mature codec with a mature and well-known licensing model.

   It is a well-established fact that not all H.264 right holders are
   MPEG-LA pool members.  H.264 is however an ITU/ISO/IEC international
   standard, developed under their respective patent policies, and all
   contributors must license their patents under Reasonable And Non-
   Discriminatory (RAND) terms.  In the field of video coding, most
   major research groups interested in patents do contribute to the
   ITU/ISO/IEC standards process and are therefore bound by those terms.

   VP8 is a much younger codec than H.264 and it is fair to say that the
   licensing situation is less clear than for H.264.  Google has
   provided their patent rights on VP8, including patents owned by 11
   patent holders [MpegLaVp8], under a open source friendly license with
   very restrictive reciprocity conditions.

   VP8 in Video Coding for Browsers in MPEG is at the time of writing in
   Draft International Standard ballot until January 2015, which is the
   next-to-last step in becoming an MPEG standard.  As such, it will
   have to follow the ISO/IEC/ITU common patent policy
   [IsoIecItuPolicy], before becoming International Standard.  IPR

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   statements in MPEG or in the ISO/IEC database [IEC-Declarations],
   received so far, contain royalty free (option 1), "Fair, Reasonable
   And Non-Discriminatory" (FRAND, option 2), and "Unwilling to grant
   license" (option 3).  Potential IPR owners that do not participate in
   this MPEG work are under no obligation to offer any license at all.
   This indicates that the licensing situation for VP8 has still not
   settled but tends toward a non-RF situation.

7.  Performance

   Comparing video quality is difficult.  Practically no modern video
   encoding method includes any bit-exact encoding where a given (video)
   input produces a specified encoded output bitstream.  Instead, the
   encoded bitstream syntax and semantics are specified such that a
   decoder can correctly interpret it and produce a known output.  This
   is true both for H.264 and VP8.  Significant freedom is left to the
   encoder implementation to choose how to represent the encoded video,
   for example given a specific targeted bitrate.  Thus it cannot in
   general be expected that any encoded video bitstream represents the
   best possible or most efficient representation, given the defined
   bitstream syntax elements available to that codec.  The actually
   achieved quality for a certain bitstream, how close it is to the
   optimally possible with available syntax, at any given bitrate rather
   depends on the performance of the individual encoder implementation.

   Also, not only is the resulting experienced video quality subjective,
   but also depends on the source material, on the point of operation
   and a number of other considerations.  In addition, performance can
   be measured vs. bitrate, but also vs. e.g. complexity - and here
   another can of worms can be opened because complexity depends on
   hardware used (some platforms have video codec accelerations), SW
   platform (and how efficient it can use the hardware) and so on.  On
   top of this comes that different implementations can have different
   performance, and can be operated in different ways (e.g. tradeoffs
   between complexity and quality can be made).  Regardless of how a
   performance evaluation is carried out it can always be said that it
   is not "fair".  This section nevertheless attempts to shed some light
   on this subject, and specifically the performance (measured against
   bitrate) of H.264 compared to VP8.

   A number of studies [H264perf1][H264perf2][H264perf3] have been made
   to compare the compression efficiency performance between H.264 and
   VP8.  These studies show that H.264 is in general performing better
   than VP8 but the studies are not specifically targeting video
   conferencing.  While constituting an independent test material
   providing some indications, those tests however do not use exactly
   the proposed profiles and levels, which calls for performing a set of
   more targeted tests.

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   Google made a comparison test between VP8 and H.264 [GooglePSNR],
   providing a set of test scripts [GoogleScripts].  That test includes
   the use of rate control for both codecs.  We believe this to be a
   comparison problem since rate control is part of the encoder, which
   as said above is typically not specified in video codec standards but
   left up to individual implementations.  The quantization parameter
   (qp) level affects the rate/distortion tradeoff in video coding.
   Comparing using fixed qp-levels is what has typically been used when
   benchmarking new codecs, for example when benchmarking HEVC [H265]
   against H.264 in the JCT-VC [JCT-VC] standardization.  We are going
   to select a codec (essentially bit stream format), not a rate control
   mechanism; once the codec is selected you can choose whatever rate
   control mechanism you wish that best suits your specific application.
   Therefore, we propose to compare the codecs with rate control off,
   using fixed quantization parameter (qp) levels.

   Ericsson made a comparison using Google's published test scripts as
   baseline and changed the parameter settings in order to make it
   possible to measure using fixed qp.  The focus of that test was to
   evaluate the best compression efficiency that could be achieved with
   both codecs since it was believed to be harder to make a fair
   comparison trying to use complexity constraints.  We used the same
   eleven sequences as in the previous Google test, but limited them to
   the first 10 seconds since they varied from 10 seconds to minutes;
   this also eased computation time.  The used video resolutions are
   640x360 @ 30 fps, 640x480 @ 30 fps, 1280x720 @ 30 fps and 1280x720 @
   50 fps.

   We used two H.264 encoder implementations:

   o  X264, which is an open-source codec that can operate in everything
      from real-time to slow

   o  JM, which is the (Joint Model) reference implementation that was
      used to develop H.264, and is very slow but attempts to be very
      efficient in terms of bits per quality

   This is a summary of the results (complete scripts and results
   available here [H264VP8Tests]):

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   | Test                             | Resulting bitrate at           |
   |                                  | equivalent quality             |
   | X264 Constrained Baseline vs VP8 | H.264 wins with 1%             |
   | JM Constrained Baseline vs VP8   | H.264 wins with 4%             |
   | X264 Constrained High vs VP8     | H.264 wins with 25%            |
   | JM Constrained High vs VP8       | H.264 wins with 24%            |

                  Table 1: Performance Comparison Results

   It is interesting to note that the measurements are more stable in
   this test; the variance of the percentages for the different
   sequences is now around 70, down from around 700 in Google's test.
   We believe this is due to the removal of the rate controller, which
   acts as noise on the measurements.

   It can also be noted that the Google method of calculating the rate
   differences does not give exactly the same numbers as the JCT-VC way
   of calculating Bjontegaard Delta bitrate (BD-rate) [PSNRdiff].  The
   main difference is that the JM score for Constrained High in the
   table above (Table 1) is around 29% better than VP8 if the JCT-VC way
   of calculating BD-rate is used.

   A rough complexity estimate can be obtained from the total running
   times for the tests:

   o  X264: 1 hour 3 minutes

   o  VP8: 2 hours 0 minutes

   o  JM: An order of magnitude slower

   Again, video quality is difficult to compare.  The authors however
   believe that the data provided in this section shows that H.264
   Constrained Baseline is at least on par with VP8, while H.264
   Constrained High seems to have a clear quality advantage.  As a final
   note, the new H.265/HEVC standard [H265] clearly outperforms all
   three, but the authors think it is premature to mandate HEVC for

8.  Profile/level

   H.264/AVC [H264] has a large number of encoding tools, grouped in
   functionally reasonable toolsets by codec profiles, and a wide range
   of possible implementation capability and complexity, specified by
   codec levels.  It is typically not reasonable for H.264 encoders and

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   decoders to implement maximum complexity capability for all of the
   available tools.  Thus, any H.264 decoder implementation is typically
   not able to receive all possible H.264 streams.  Which streams can be
   received is described by what profile and level the decoder conforms
   to.  Any video stream produced by an H.264 encoder must keep within
   the limits defined by the intended receiving decoder's profile and
   level to ensure that the video stream can be correctly decoded.

   Profiles can be "ranked" in terms of the amount of tools included,
   such that some profiles with few tools are "lower" than profiles with
   more tools.  However, profiles are typically not strictly supersets
   or subsets of each other in terms of which tools are used, so a
   strict ranking cannot be defined.  It is also in some cases possible
   to express compliance to the common subset of tools between two
   different profiles.  This is fairly well described in [RFC6184].

   When choosing a Mandatory To Implement codec, it is desirable to use
   a profile and level that is as widely supported as possible.
   Therefore, H.264 Constrained Baseline Profile Level 1.2 MUST be
   supported as Mandatory To Implement video codec.  This is possible to
   support with significant margin in hardware devices (Section 4) and
   should likely also not cause performance problems for software-only
   implementations.  All Level definitions (Annex A of [H264]) include a
   maximum framesize in macroblocks (16*16 pixels) as well as a maximum
   processing requirement in macroblocks per second.  That number of
   macroblocks per second can be almost freely distributed between
   framesize and framerate.  The maximum framesize for Level 1.2
   corresponds to 352*288 pixels (CIF).  Examples of allowed framesize
   and framerate combinations for Level 1.2 are CIF (352*288 pixels) at
   15 Hz, QVGA (320*240 pixels) at 20 Hz, and QCIF (176*144 pixels) at
   60 Hz.

   Recognizing that while the above profile and level will likely be
   possible to implement in any device, it is also likely not sufficient
   for applications that require higher quality.  Therefore, it is
   RECOMMENDED that devices and implementations that can meet the
   additional requirements also implement at least H.264 Constrained
   High Profile Level 1.3, logically extended to support 720p resolution
   at 30 Hz framerate, but in formal specification text it would have to
   be expressed as a restriction on a higher level.

   Note that the lowest non-extended Level that support 720p30 is Level
   3.1, but fully supporting Level 3.1 also requires fairly high
   bitrate, large buffers, and other encoding parameters included in
   that Level definition that are likely not reasonable for the targeted
   communication scenario.  This method of extending a lower level in
   SDP (Section 9) with a smaller set of applicable parameters is fully

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   in line with [RFC6184], and is already used by some video
   conferencing vendors.

   When considering the main WebRTC use case, real-time communication,
   the lack of need to support interlaced image format in that context,
   the limited use of bi-predictive (B) pictures, and the added
   implementation and computation complexity that comes with interlace
   and B-picture handling suggests that Constrained High Profile should
   be preferred over High Profile as optional codec.  Note also that
   while Constrained High Profile is currently less supported in devices
   than High Profile, any High Profile decoder will be capable of
   decoding a Constrained High Profile bitstream since it is a subset of
   High Profile.  To make a High Profile encoder support Constrained
   High Profile encoding, it will have to turn off interlace encoding
   and turn off the use of bi-prediction.

   The below table summarizes the H.264 video encoding features used by
   Constrained Baseline Profile (CBP) and Constrained High Profile
   (CHP).  For more information on the listed features, see

          | Feature                            | CBP   | CHP   |
          | Bit depth per sample               | 8     | 8     |
          | Chroma formats                     | 4:2:0 | 4:2:0 |
          | Flexible Macroblock Ordering (FMO) | No    | No    |
          | Arbitrary Slice Ordering (ASO)     | No    | No    |
          | Redundant Slices                   | No    | No    |
          | Data Partitioning                  | No    | No    |
          | SI and SP slices                   | No    | No    |
          | Interlaced coding                  | No    | No    |
          | B slices                           | No    | No    |
          | CABAC entropy coding               | No    | Yes   |
          | Monochrome 4:0:0                   | No    | Yes   |
          | 8x8 vs. 4x4 transform adaptivity   | No    | Yes   |
          | Quantization scaling matrices      | No    | Yes   |
          | Separate color QP control          | No    | Yes   |
          | Separate color plane coding        | No    | No    |
          | Predictive lossless coding         | No    | No    |
          | Weighted prediction                | No    | Yes   |

9.  Negotiation

   Given that there exist a fairly large set of defined profiles and
   levels (Section 8) in the H.264 specification, the probability is
   rather low that randomly chosen H.264 encoder and decoder

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   implementations have exactly matching capabilities.  In any
   communication scenario, there is therefore a need for a decoder to be
   able to convey its maximum supported profile and level that the
   encoder must not exceed.

   In addition and depending on the wanted use case and the conditions
   that apply at a certain communication instance, there may also be a
   need to describe the currently wanted profile and level at the start
   of the communication session, which may be lower than the maximum
   supported by the implementation.  In this scenario it may also be of
   interest to communicate from the encoder to the decoder both which
   profile and level that will actually be used and what is the maximum
   supported profile and level.  The reason to communicate not only the
   starting point but also the maximum assumes that communication
   conditions may change during the conditions, maybe multiple times,
   possibly making another profile and level be a more appropriate

   Communication of maximum supported profile and level is the only
   mandatory SDP [RFC4566] parameter in the H.264 payload format
   [RFC6184], which also includes a large set of optional parameters,
   describing available use (decoder) and intended use (encoder) of
   those parameters for a specific offered [RFC3264] stream.

   If the above mentioned (Section 8) capability for 720p30 is supported
   as an extension to Constrained High Profile Level 1.3 (or higher),
   the logical level extension SHOULD be signaled in SDP using the
   following parameters as defined in section 8.1 of [RFC6184]:

   o  profile-level-id=640c0d (or corresponding to a higher Level of
      Constrained High profile)

   o  max-fs=3600 (or greater)

   o  max-mbps=108000 (or greater)

   o  max-br=768 (or greater, whatever the device implementation can

10.  Summary

   H.264 is widely adopted and used for a large set of video services.
   This in turn is because H.264 offers great performance, reasonable
   licensing terms (and manageable risks).  As a consequence of its
   adoption for many services, a multitude implementations in software
   and hardware are available.  Another result of the widespread
   adoption is that all associated technologies, such as payload
   formats, negotiation mechanisms and so on are well defined and

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   standardized.  In addition, using H.264 enables interoperability with
   many other services without video transcoding.

   We therefore propose to the WG that H.264 shall be mandatory to
   implement for all WebRTC endpoints that support video, according to
   the details described in Section 8 and Section 9.

11.  IANA Considerations

   This document makes no request of IANA.

   Note to RFC Editor: this section may be removed on publication as an

12.  Security Considerations

   No specific considerations apply to the information in this document.

13.  Acknowledgements

   All that provided valuable descriptions, comments and insights about
   the H.264 codec on the IETF mailing lists.

14.  References

14.1.  Normative References

   [H264]     ITU-T Recommendation H.264, "Advanced video coding for
              generic audiovisual services", April 2013,

   [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

   [RFC4566]  Handley, M., Jacobson, V., and C. Perkins, "SDP: Session
              Description Protocol", RFC 4566, July 2006.

   [RFC6184]  Wang, Y., Even, R., Kristensen, T., and R. Jesup, "RTP
              Payload Format for H.264 Video", RFC 6184, May 2011.

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14.2.  Informative References

   [AirPlay]  Apple Inc, "AirPlay Overview: About AirPlay", September
              2012, <https://developer.apple.com/library/ios/documentati

              Apple Inc., "AV Foundation Programming Guide", March 2014,

              BlackBerry Limited, "Supported codecs - BlackBerry
              Native", September 2014,

              Microsoft Open Technologies, Inc., "CU-RTC-Web-Video",
              July 2013,

   [DLNA]     DLNA(R), "Technical Overview", 2013, <http://www.dlna.org/

   [FF33]     "Cisco's OpenH264 Now Part of Firefox", October 2014,

   [GSMA]     "GSM Association", 2014, <http://www.gsma.com/>.

              GSM Association, "WebRTC Codecs DRAFT v1.3", September

              Google, "Supported Media Types - Google Cast", October
              2013, <https://developers.google.com/cast/

              The WebM Project, "VP8 Results", April 2013,

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              The WebM Project, "VP8 vs H.264 Test Scripts", April 2013,

              Ericsson, "More H.264 vs VP8 tests", June 2013,

              Vatolin, D., "MPEG-4 AVC/H.264 Video Codecs Comparison
              2010 - Appendixes", , May 2010,

              Shah, K., "Implementation, performance analysis and
              comparison of VP8 and H.264.", University of Texas at
              Arlington Department of Electrical Engineering, 2011,

              De Simone, F., Goldmann, L., Lee, J., and T. Ebrahimi,
              "Performance analysis of VP8 image and video compression
              based on subjective evaluations", Ecole Polytechnique
              F'd'rale de Lausanne (EPFL) , Aug 2011,

   [H265]     ITU-T Recommendation H.265, "High Efficiency Video
              Coding", April 2013,

              International Electrotechnical Commission, "List of IEC
              patent declarations received by IEC", October 2014,

   [IR39]     GSM Association, "IMS Profile for High Definition Video
              Conference (HDVC)", May 2013,

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   [IR94]     GSM Association, "IMS Profile for Conversational Video
              Service", May 2013, <http://www.gsma.com/newsroom/

              Wikipedia, "H.264/MPEG-4 AVC products and
              implementations", September 2014,

              ISO, "ISO/IEC/ITU common patent policy", April 2007,

   [JCT-VC]   ITU-T, "JCT-VC - Joint Collaborative Team on Video
              Coding", <http://www.itu.int/en/ITU-T/studygroups/2013-

   [MPEGLA]   MPEG LA, "MPEG LAs AVC License Will Not Charge Royalties
              for Internet Video that is Free to End Users through Life
              of License", MPEGLA News Release, August 2010,

              MPEG LA, "AVC Patent Portfolio License Briefing", May
              2009, <http://www.mpegla.com/main/programs/avc/Documents/


              Android, "MediaCodec | Android Developers", October 2014,

              Wi-Fi Alliance(R), "What formats does Miracast support?",
              2013, <http://www.wi-fi.org/knowledge-center/faq/

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              O'Reilly, T., "Google and MPEG LA Announce Agreement
              Covering VP8 Video Format", March 2013,

              "OpenH264", 2014, <http://www.openh264.org/>.

   [OpenMAX]  Khronos, "OpenMAX - The Standard for Media Library
              Portability", 2014, <https://www.khronos.org/openmax/>.

              Bjontegaard, G., "Calculation of Average PSNR Differences
              between RD-Curves", ITU-T SG16 Q.6 Document VCEG-M33,
              April 2001.

              "3rd Generation Partnership Project",

   [WEBM]     The WebM Project, "SoCs Supporting VP8/VP9", October 2014,

   [WiDi]     Intel Corporation, "Intel(R) Wireless Display and Intel(R)
              Pro Wireless Display", October 2013,

              Wikipedia, "H.264/MPEG-4 AVC", October 2013,

   [Woon]     Polycom, "Polycom Delivers Open Standards-Based Scalable
              Video Coding (SVC) Technology, Royalty-Free to Industry",
              October 2012,

Authors' Addresses

   Bo Burman
   Farogatan 6
   Stockholm  16480

   Email: bo.burman@ericsson.com

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   Markus Isomaki
   Keilalahdentie 2-4
   Espoo  FI-02150

   Email: markus.isomaki@nokia.com

   Bernard Aboba
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052

   Email: bernard_aboba@hotmail.com

   Gaelle Martin-Cocher
   BlackBerry Ltd
   1875 Buckhorn Gate
   Mississauga, ON  L4W 5P1

   Email: gmartincocher@blackberry.com

   Giri Mandyam
   Qualcomm Innovation Center

   Email: mandyam@quicinc.com

   Xavier Marjou
   2, avenue Pierre Marzin
   Lannion  22307

   Email: xavier.marjou@orange.com

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   Cullen Jennings
   170 West Tasman Drive
   San Jose, CA  95134
   United States

   Email: fluffy@cisco.com

   Jonathan Rosenberg
   170 West Tasman Drive
   San Jose, CA  95134

   Email: jdrosen@cisco.com

   David Singer

   Email: singer@apple.com

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