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[Bug 13544] New: Video: <track> element should allow support of more than one format without content sniffing

From: <bugzilla@jessica.w3.org>
Date: Wed, 03 Aug 2011 00:09:35 +0000
To: public-html-bugzilla@w3.org
Message-ID: <bug-13544-2486@http.www.w3.org/Bugs/Public/>

           Summary: Video: <track> element should allow support of more
                    than one format without content sniffing
           Product: HTML WG
           Version: unspecified
          Platform: PC
        OS/Version: All
            Status: NEW
          Severity: normal
          Priority: P2
         Component: HTML5 spec (editor: Ian Hickson)
        AssignedTo: ian@hixie.ch
        ReportedBy: silviapfeiffer1@gmail.com
         QAContact: public-html-bugzilla@w3.org
                CC: mike@w3.org, public-html-wg-issue-tracking@w3.org,

The <track> element as specified right now is similar to the <img> element for
detecting what mime type the resource specified in @src is: browsers have to do
content sniffing to identify the mime type of the resource.

If all Web browsers only implement support for a single format, we won't have a
problem. However, I know that several browser vendors want to support multiple
external text track formats, including WebVTT, TTML, and possibly others.

The need to content sniff is a problem for this element when on mobile devices
and when the list of alternative tracks becomes rather long. This can be the
case for videos that have subtitles in many languages, such as e.g.
http://www.youtube.com/watch?v=QRS8MkLhQmM&cc=1 .

To solve this, the suggestion is to change the content model of the <track>
element from being empty to allowing <source> as children. For example:

<video controls src="video.webm">
  <track label="English Captions" kind="captions" srclang="en-US">
    <source src="cap_en.ttml" type="text/ttml">
    <source src="cap_en.vtt" type="text/vtt">
    <source src="cap_en.srt" type="text/srt">
    <source src="cap_en.mpsub" type="text/mpsub">

I'd be curious what people think about this option.

FYI: MPSub is MPlayer's subtitle format:

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Received on Wednesday, 3 August 2011 00:09:37 UTC

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