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519 lines
24 KiB
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
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<h1>W3C Video on the Web Workshop <span class="baseline">12-13 December 2007, San Jose, California and Brussels, Belgium</span></h1>
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</div>
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<div id="navigation">
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<ul>
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<li><a href="http://www.w3.org/Consortium/">About W3C</a></li>
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<li><a href="/2007/08/video/">Call for Participation</a></li>
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<li><a href="papers">Papers</a></li>
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<li class='current'>Report</li>
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<li><a href="agenda">Agenda</a></li>
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</ul>
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</div>
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<div id="main">
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<p class="logo" style="float:right;margin-left:1em;"><a href="/"><img src="/Icons/WWW/w3c_home_nb" alt="W3C" height="48" width="72" /></a></p>
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<h2 id="report" style="clear:left;">Workshop Report</h2>
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<!-- content beg -->
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<div class='report'> <p>W3C organized a workshop on Video on the Web
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in December 2007, hosted by Cisco Systems, in order to share current
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experiences and examine the technologies. <a href='papers.html'>42
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position papers</a> were submitted for the Workshop and <a href='minutes.html'>37
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organizations</a> attended the event from a wide range of applications:
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content producers, network companies, research institutes, hardware
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vendors, video platforms, browser vendors, users, etc. The meeting was
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hosted in San Jose, California and Brussels, Belgium, with both
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locations linked with high definition video.</p>
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<div class="subtoc">
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<h3>Table of Contents</h3>
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<ol>
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<li><a href="#Summary">Summary</a></li>
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<li><a href="#Introduction">Introduction</a></li>
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<li><a href="#Metadata">Metadata</a></li>
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<li><a href="#Video_codec_for_the_Web">Video codec for the Web</a></li>
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<li><a href="#Deep_linking_into_Video_content">Addressing into Video
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content</a>
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<ol>
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<li><a href="#Temporal_Addressing">Temporal Addressing</a></li>
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<li><a href="#Spatial_Addressing">Spatial Addressing</a></li>
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</ol>
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</li>
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<li><a href="#DRM">Digital Rights Management</a></li>
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<li><a href="#Other_Topics">Other Topics of Interest</a>
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<ol>
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<li><a href="#Accessibility">Accessibility</a></li>
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<li><a href="#HTML_video_tag">HTML <code>video</code> tag</a></li>
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<li><a href="#API">APIs for Controlling Video</a></li>
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<li><a href="#Content_Delivery">Content Delivery and Network
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Traffic</a></li>
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</ol>
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</li>
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<li><a href="#Next_steps">Next steps</a>
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<ol>
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<li><a href='#step1'>8.1 Codecs and containers</a></li>
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<li><a href='#step2'>8.2 Metadata</a></li>
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<li><a href='#step3'>8.3 Addressing</a></li>
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<li><a href='#step5'>8.4 Best practices for video and audio content</a></li>
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<li><a href='#step4'>8.5 Cross-group coordination</a></li>
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</ol>
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</li>
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</ol>
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</div>
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<h2 id="Summary">1. Summary</h2>
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<div class="image noprint">
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<p class="img" style="width: 274px"><a href='http://www.flickr.com/photos/rwfreund/2115753881/'><img src="/2008/01/camera.jpg" title="Camera"
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alt="Camera" /></a>
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<br />
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<span class="source">Photo credit: <a
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href="http://www.flickr.com/photos/rwfreund/">Bob Freund</a></span></p>
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</div>
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<p>Online video content and demand is increasing rapidly and the trend will
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continue for at least a few years. Workshop participants gathered to discuss
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and to share current experiences and to examine the technologies. Some of the
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key issues participants discussed related to:</p>
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<ul>
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<li><strong>Metadata</strong>: searching and discovering video is difficult
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with the volume of online video. Having <em>data about data</em>, whether those are
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automatically generated or manually added, is important, especially when
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considering the value added by metadata provided by users.</li>
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<li><strong>Video codec</strong>: several W3C Working Groups are struggling
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with the issue of recommending a baseline video codec for the World Wide
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Web. W3C should continue to investigate the existing video codecs.</li>
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<li><strong>Addressing</strong>: in order to make video a first-class
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object on the World Wide Web, one should be able to identify spatial and
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temporal clips. Having global identifiers for clips would allow
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substantial benefits, including in linking, bookmarking, caching and
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indexing. None of the existing solutions is fully satisfactory or
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provides a unique resource identifier for clips.</li>
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<li><strong>Content protection</strong>: many content producers feel that
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the success of video online is tied to the ability to manage digital
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rights associated with the media. While W3C will not investigate the
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issue of enforcement, it should look into metadata for digital
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rights.</li>
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</ul>
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<p>The Workshop was informative and energetic, and it is anticipated that the
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W3C Team will work with the Membership to propose a new W3C Activity to
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continue studying video on the Web, including, for example, Guidelines for
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publishing and deploying online video.</p>
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<h2 id="Introduction">2. Introduction</h2>
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<div class="image noprint">
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<p class="img" style="width: 167px"><a href='http://www.flickr.com/photos/roessler/2109755736/'><img src="/2008/01/chris_takes_a_picture_2.jpg"
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alt="W3C Video Workshop Telepresence" title="W3C Video Workshop Telepresence"
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/></a>
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<br />
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<span class="source">Photo credit: <a
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href="http://www.flickr.com/photos/49504282@N00/">Chris Lilley</a></span></p>
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</div>
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<p>Online video has become omnipresent on the Web in the recent years.
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YouTube, launched in 2005, represented 4% of traffic on high-Internet lines
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on the Comcast network by the end of 2006. Online video appeals to the Web
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audience as it lets people go beyond the capabilities of traditional
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television: more people can distribute video ("the long tail") and social
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networking allows others in the community to comment, and even reply with
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other video. The number of user generated video uploads per day is expected
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to go from 500,000 in 2007 to 4,800,000 in 2011 (<a href='http://www.ripcode.com/prodForm.php'><cite>Transcoding Internet and Mobile Video: Solutions for the Long Tail</cite></a>, IDC, September 2007). The demand for
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online video content also keeps increasing. Recent studies indicate that the
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number of U.S. internet users who have visited a video-sharing site increased
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by 45% in 2007, and the daily traffic to such sites has doubled (<a
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href="http://www.pewinternet.org/PPF/r/232/report_display.asp"><cite>PEW Internet Project Data Memo</cite></a>, PEW/Internet, January 2008).
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Expectations are quickly evolving to the point where people want videos to
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publish and view at any time and from any device. These rapid changes are
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posing challenges to the underlying technologies and standards that support
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the platform-independent creation, authoring, encoding/decoding, and
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description of video. To ensure the success of video as a "first class
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citizen" of the Web, the community needs to build a solid architectural
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foundation that enables people to create, navigate, search, and distribute
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video, and to manage digital rights.</p>
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<p>W3C has been involved in the area of Video on the Web since 1996,
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and organized two workshops around this in the past: <cite><a
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href="http://www.w3.org/AudioVideo/RTMW96.html">Real Time Multimedia
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and the Web</a></cite> (October 1996) and <cite><a
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href="http://www.w3.org/Architecture/1998/06/Workshop/">Television and
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the Web</a></cite> (June 1998). SMIL (Synchronized Multimedia
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Integration Language), first published in June 1998, provides support
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for embedding audio and video content. W3C continues to work on the
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integration of video with other media, synchronized video content in
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graphics with SVG (Scalable Vector Graphics), and direct support for
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video and audio in Web browsers with the proposal for a video element
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in HTML 5.</p>
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<h2 id="Metadata">3. Metadata</h2>
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<p>Workshop participants expressed great interest on the subject of
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metadata for video and audio content. This was the topic that
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generated the most discussion and interest at the Workshop, with use
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cases coming from several perspectives. The major use cases for
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adding metadata were content labeling, search, and
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discovery. Anticipating the increase in online video and audio in the
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upcoming years, participants observed that it will become
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proportionally more difficult for viewers to find the content. It was
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noted that metadata comes from several places: content creator,
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publisher, third-party, or users. Some of the metadata will be
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automatically produced (face, text or object recognition) and others
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will be manually added. Some of the metadata will be part of the
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content (in the format container) or external to the content. Adding
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user-generated metadata can increase tremendously the value of the
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content. Of course, the quality of such metadata will highly vary,
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especially in non-trusted environments. There was a wide range of
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interest for adding specific metadata: title, author, year, cast,
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city, digital rights, ratings, tagging, etc. It was pointed out that
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multiple video formats can be available for the same video, at
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different data rates. Also, the availability of the metadata will
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depend on the delivery chain and the player used. For example,
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transcoding often means that the metadata will get dropped.</p>
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<p>Several more or less complex solutions exist in this domain: MPEG 7, SMIL,
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iTunes XML, Yahoo! MediaRSS, CableLabs VOD Metadata Content, etc. Not many
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online video distributors are making use of metadata or facilitating the use
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of by others, either in the professional world or in the world of user
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generated video. Despite the general interest in metadata, no clear direction
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came from the workshop. Given its Semantic Web activity, the W3C should
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continue to investigate in this area, while taking into account the existing
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solutions.</p>
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<h2 id="Video_codec_for_the_Web">4. Video codec for the Web</h2>
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<div class="image noprint">
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<p class="img"><img src="/2008/01/video-container_2.png"
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title="Format container and codecs" alt="Format container and codecs" />
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</p>
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</div>
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<p>The issue of video codec has been around for a few years — for example,
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the SMIL 3 specification attempts to recommend a baseline video codec based on SMIL 1 and 2
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experience — but surfaced more preeminently in relation to HTML 5. The <a
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href="http://www.w3.org/TR/html5/">HTML 5 Working Draft</a>, which includes a
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proposal for embedding and controlling <a
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href="http://www.w3.org/TR/2008/WD-html5-20080122/#audio">audio</a> and <a
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href="http://www.w3.org/TR/2008/WD-html5-20080122/#video">video</a> content,
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has attracted a lot of attention on the choice of video codec. The HTML
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Working Group seems inclined to recommend a baseline video codec, there is
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not yet consensus on which codec to recommend. The Group has elaborated a
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number of requirements, such as <q>compatibility with the open source
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development model</q> or <q>no additional submarine patent risk</q> (see
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section 3.14.7.1, <cite><a
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href="http://www.w3.org/TR/2008/WD-html5-20080122/#video0">Video and audio
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codecs for video elements</a></cite>, HTML 5), some of which may be
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incompatible.</p>
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<!-- forward reference to thml video tag section -->
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<p>Several existing video codecs were discussed by the Workshop
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participants. H.264 has been adopted a lot of the industry. The mobile
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industry has adopted H.264, at least in 3GPP/3GPP2 standards. Adobe
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recently announced support for H.264 in their Flash product. However,
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the H.264 has licensing requirements that are incompatible with open
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source requirements and is not a royalty-free codec (which makes it
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incompatible with the <a
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href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Licensing">goals</a>
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of the W3C Patent Policy). Until recently, the HTML 5 specification
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was indicating that browser implementations suggested that browser
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implementations support the Theora codec. There are currently
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uncertainties about the IPR requirements surrounding the Theora codec,
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and organizations are concerned about taking additional submarine
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patent risks. Of course, one can claim that not all risks are known
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for the H.264 video codec either. It should also be noted that several
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patents around these video technologies expire every year. Other codec
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candidates to consider are Dirac, VC-1, or older codecs such as H.261
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or H.263. Video codecs keep evolving and today's codec will be
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different from tomorrow's codec. The BBC submitted the intra-only
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portion of Dirac (“Dirac 1.0.0”) to SMPTE and it is expected to become a
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standard in the upcoming few months, as “VC-2”. BBC claims that it is
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<a href='http://dirac.sourceforge.net/specification.html'>suitable for
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professional applications</a>. The BBC also released the full version
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of Dirac (“Dirac 2.1.0”) on 24 January 2008, which includes motion
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compensation and is <a
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href='http://dirac.sourceforge.net/specification.html'>suitable for
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broadcasting and streaming</a>. The Joint Video Team (JVT) of ISO/ITU
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released a scalable profile of H.264 in the spring last year and
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started the work on H.265.</p>
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<p>For large video content producers, the end user experience is more
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important than the goal of a single baseline codec. The end user experience
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includes widely available players, codecs whose functionality provides a good
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viewing experience, and other issues related to ease of use. Most will take
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Flash Video for granted in fact, or will deploy their own video player, using
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a codec that fits the desired quality of the content (such as the VP7 On2
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codec). Individual content producers — the home video crowd — still
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suffer from the lack of a universally supported set of codecs, which makes it
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challenging to publish video on the Web and to be sure that almost anyone can
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view it in commonly available browsers. One should be able to publish a video
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the same way one publishes an image nowadays. The sentiment shared among
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several participants was that W3C should gather the relevant parties and
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continue to explore the issue. The participants of the Workshop did not
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discuss issues associated with audio codecs, mostly due to the predominant
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concerns with video codecs. Analogous audio codec issues also merit
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investigation.</p>
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<h2 id="Deep_linking_into_Video_content">5. Addressing into Video content</h2>
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<p>In order to make video and audio real first-class objects on the
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Web, one should be able to link from and to media, the same way
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authors can make hyperlinks between Web pages. It also allows other
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use cases, such as video highlights, search results, mashing, or
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caching. It also provides an identifier that can then be reused to
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attach metadata. The discussion covered spatial and temporal
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addressing, as well as a combination of the two.</p>
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<h3 id="Temporal_Addressing">5.1 Temporal Addressing</h3>
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<div class="image noprint">
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<p class="img"><img src="/2008/01/timbl_movie_2.png" title="Movie tape"
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alt="Movie tape" />
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</p>
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</div>
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<p>Temporal addressing provides the ability to reference a time point,
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or a segment of time, in video and audio content: a normal play time
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(or time offset), a framed-based time, or an absolute time. It allows
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the media player to jump to the specified time or frame, or only to
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play a segment of file. RFC 2326 (RTSP) defines the notion of normal
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play time, the stream absolute position relative to the beginning of
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the video. SMPTE time codes (SMPTE 12M-1999 Television, Audio and Film
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— Time and Control Code) defines the notion of frame-level
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accuracy. Absolute time uses UTC.</p>
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<p>Temporal addressing approaches in <a
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href="http://www.w3.org/TR/SMIL/">SMIL</a>, <a
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href="http://www.chiariglione.org/mpeg/standards/mpeg-7/mpeg-7.htm">MPEG-7</a>,
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<a
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href="http://www.chiariglione.org/mpeg/standards/mpeg-21/mpeg-21.htm">MPEG-21</a>
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and <a
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href="http://www.annodex.net/TR/draft-pfeiffer-temporal-fragments-03.html">temporal
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URI</a>.</p>
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<p>Both SMIL and MPEG-7 require an indirection: one needs to get the
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XML description containing the temporal information before fetching
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the video content. It should be noted, thought it was not mentioned at
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the Workshop, that even HTML 5 includes the notion of time offset and
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time segment.</p>
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<p>On the other hand, the MPEG-21 and Temporal URI approaches rely on
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defining a URI syntax and thus don't rely on an additional XML description.
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However, these approaches also have limitations:</p>
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<ul>
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<li><p>They lack the ability to represent complex fragments, especially
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when combining temporal and spatial addressing.</p>
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</li>
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<li><p>When using the fragment identifier component syntax of a URI, it is
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dependent on the media type of the retrieved representation (see section
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3.5, Fragment, RFC 3986). For example, the MPEG-21 URI syntax is tied to
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the MPEG container. Thus, it would be difficult to apply one generic
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fragment identifier to the existing video or audio codecs.</p>
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</li>
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</ul>
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<h3 id="Spatial_Addressing">5.2 Spatial Addressing</h3>
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<div class="image noprint">
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<p class="img" style="width: 250px"><a href='http://www.flickr.com/photos/rwfreund/2116534410/'><img src="/2008/01/beth_2.jpg"
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title="Beth, the audience, Belgium, her pitch, and herself"
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alt="Beth, the audience, Belgium, her pitch, and herself" /></a>
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<br />
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<span class="source">Photo credit: <a
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href="http://www.flickr.com/photos/rwfreund/">Bob Freund</a></span></p>
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</div>
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<p>Spatial addressing provides the ability to reference a region in a video
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frame. Information can then be attached to the particular region or, when
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combined with timed-based addressing, objects can then be tracked in the
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video.</p>
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<p>Three solutions were mentioned at the workshop: SVG, SMIL and
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MPEG-7. All solutions require an indirection for accessing the region
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in the video.</p>
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<h2 id="DRM">6. Digital Rights Management</h2>
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<p>Several of the participants at the Workshop were interested in the topic
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of Digital Rights management, an issue particularly important in the music
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and the motion picture and television industries. This topic touched on two
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subjects mentioned above: video codec and metadata. A baseline video codec
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and format container for online video content would only satisfy some of the
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content producers if it is associated with a digital rights management (DRM)
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solution. No one suggested that W3C should develop a DRM system but future work
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at W3C needs to keep DRM issues in mind. It was noted that the choice of
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video codec doesn't need to be tied to the choice of DRM system, since both
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technologies are independent in general. There was also some interest in
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investigating further the area of metadata for digital rights (copyright and
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licensing).</p>
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<h2 id="Other_Topics">7. Other Topics of Interest</h2>
|
|
|
|
<p>Other topics of interest listed in this section were mentioned or
|
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discussed at the workshop.</p>
|
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|
|
<h3 id="Accessibility">7.1 Accessibility</h3>
|
|
|
|
<p>W3C has a mission to ensure that the Web is accessible to people
|
|
with disabilities; naturally this includes video content. A vast
|
|
majority of online video and non-professional content lacks
|
|
captioning, sign language, or video description. The Web Content
|
|
Accessibility Guidelines 1.0 were published in May 1999 and there are
|
|
several solutions for captioning/video description currently
|
|
available. Extensions have been made to support captioning using the
|
|
W3C Timed Text (DXFP) format in combination with the Flash player, but
|
|
DXFP itself is not yet a W3C Recommendation. The Flash Player 9
|
|
adopted 3GPP TS 26.245 as its Timed Text format. SMIL 3.0 introduced
|
|
SMILText, which can also be used to captioning/subtitling.</p>
|
|
|
|
<h3 id="HTML_video_tag">7.2 HTML <code>video</code> tag</h3>
|
|
|
|
<p>The HTML <code>video</code> tag was mentioned several times during the
|
|
Workshop. The primary focus of the discussion was around the baseline video
|
|
codec but several participants were concerned with the introduction of
|
|
yet-another-tag for embedding and controlling video content, especially since
|
|
the SYMM Working Group has already published a specification that addresses
|
|
timing and synchronization. The HTML Working Group introduced the notion of
|
|
cue range in their specification and care should be taken to ensure the
|
|
compatibility between the two models. No in-depth discussion happened at the
|
|
Workshop on this issue and the best recommendation at this time is to ensure
|
|
that the SYMM and HTML Working Groups coordinate their actions.</p>
|
|
|
|
<h3 id="API">7.3 APIs for Controlling Video</h3>
|
|
|
|
<p>The control of video content using APIs was a use case in several
|
|
presentations and the . Both SMIL and HTML specifications are
|
|
providing solutions to start, stop, or pause a video. Work is still
|
|
happening in the HTML specification to extend the media API. A more
|
|
extended API, the <a
|
|
href='http://wiki.xiph.org/index.php/OggPlayJavascriptAPI'>draft
|
|
API</a> for the Ogg Play Firefox plugin, was presented at the
|
|
workshop. </p>
|
|
|
|
<h3 id="Content_Delivery">7.4 Content Delivery and Network Traffic</h3>
|
|
|
|
<p>The major issue of delivering video content over the Internet and the Web
|
|
is network traffic scalability. While it's easy to deploy a Web server to
|
|
deliver HTML pages and images, video content and its bandwidth requirements
|
|
introduced an entirely new dimension. Progressive HTTP, Content Delivery
|
|
Networks, streaming media servers, or P2P technologies are among the
|
|
solutions with different cost of deployment and bandwidth. P2P technologies
|
|
have a significant impact on the network of existing ISPs, forcing them to
|
|
rethink the way they allocate the bandwidth among their users.</p>
|
|
|
|
<h2 id="Next_steps">8. Next steps</h2>
|
|
|
|
<p>
|
|
Five major areas of possible work emerged from the Workshop (the
|
|
first three discussed in detail): video codecs, metadata,
|
|
addressing, cross-group coordination and best practices for video
|
|
content.
|
|
</p>
|
|
|
|
<h3 id='step1'>8.1 Codecs and containers</h3>
|
|
|
|
<p>
|
|
The W3C team will work with interested parties to evaluate
|
|
the situation with regards to video codecs, and what, if anything, W3C
|
|
can do to ensure that codecs, containers, etc. for the Web encourage
|
|
the broadest possible adoption and interoperability.
|
|
</p>
|
|
|
|
<h3 id='step2'>8.2 Metadata</h3>
|
|
|
|
<p>Talks at the Workshop highlighted a number of metadata standards in
|
|
the space (and the number is part of the problem). Still, there was
|
|
high interest in this area. One direction would be to create a Working Group
|
|
tasked to come up with:</p>
|
|
<ol>
|
|
<li>a <em>simple</em> common ontology between the existing standards;</li>
|
|
<li>defines a mapping between this ontology and existing
|
|
standards;</li>
|
|
<li>defines a roadmap for extending the ontology, including information
|
|
related to copyright and licensing rights.</li>
|
|
</ol>
|
|
|
|
<h3 id='step3'>8.3 Addressing</h3>
|
|
|
|
<p>W3C should also consider creating a Group to investigate the
|
|
important issue of addressing. The goal would be to:</p>
|
|
<ol>
|
|
<li>provide a URI syntax for temporal and spatial addressing;</li>
|
|
<li>investigate how to attach metadata information to spatial and
|
|
temporal regions when using RDF or other existing specifications, such
|
|
as SMIL or SVG.</li>
|
|
</ol>
|
|
|
|
<h3 id='step5'>8.4 Best practices for video and audio content</h3>
|
|
|
|
<p>A Group working on guidelines and best practices for effective
|
|
video and audio content on the Web could be useful, and would look at
|
|
the entire existing delivery chain from producers to end-users, from
|
|
content delivery, to metadata management, accessibility or device
|
|
independence.</p>
|
|
|
|
<h3 id='step4'>8.5 Cross-group coordination</h3>
|
|
|
|
<p>Several existing W3C Working Groups are working on video-related
|
|
issues and there is a need for coordination (controls, layouts,
|
|
etc.):</p>
|
|
<ol>
|
|
<li>Video and CSS (layout and layering);</li>
|
|
<li>Video and SMIL, SVG or HTML (effects, transforms, codecs, playback, API);</li>
|
|
<li>Video and WAI (accessibility)</li>
|
|
<li>Video and browsers and plugins (for device independence and
|
|
managing plug-n-play specialized codecs that match various end-user
|
|
experience needs within the browser)</li>
|
|
</ol>
|
|
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|
</div>
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<!-- footer beg -->
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<div id="footer">
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<address>For more information, contact <span class="vcard"><a class="url fn" href="http://www.w3.org/People/LeHegaret/">Philippe Le Hégaret</a>, W3C Contact</span><br />
|
|
<small>$Date: 2008/04/08 20:43:53 $</small></address>
|
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</div>
|
|
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