[Webkit-unassigned] [Bug 110479] [Meta] Implement support for TTML

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=110479





--- Comment #9 from Silvia Pfeiffer <silviapf at chromium.org>  2013-02-21 18:21:11 PST ---
(In reply to comment #8)
> I would not agree with a number of your above statements:
> 
> * that TTML content needs to be translated into a list of cues (as currently defined)
> * that TTML content needs to be mapped to HTML or CSS
> * that it is impossible to implement TTML without these clarifications
> * that it is impossible to implement TTML compatibly between browsers
> 
> It may very well be possible to translate a profile of TTML, e.g., SMPTE-TT or SDP-US, into the current definition of text track cues, and that may be the first step in implementing support for such a profile. But it isn't necessary to do this in order to implement a compliant TTML presentation processor that is able to render a <track/> element that references a TTML resource.


<track> is a replaced element as listed here: http://www.w3.org/TR/html5/single-page.html#replaced-elements . Replaced elements are mapped into the DOM through mapping to an Object. 

<track> is mapped to a TextTrack object.
http://www.w3.org/TR/html5/single-page.html#the-track-element

A TextTrack object consists of a TextTrackCueList for active and for parsed cues.
http://www.w3.org/TR/html5/single-page.html#texttrack

I fail to understand how you can represent TTML in the browser without making use of these constructs that <track> stands for.


> Since IE10 does implement some level of support for TTML, it would be worth learning if they attempt to map to HTML/CSS and TextTrackCues as you suggest.

I don't have a Windows7 machine and IE10 at hand to test it, but I am 99% sure that the parsed cues are mapped into a TextTrackCueList both for TTML and WebVTT. Since IE10 only supports simple captions (starttime, endtime, text) and no formatting, all they had to do was to map the <p> elements into cues. That's the simple part of the mapping, but it's a start.

You can experiment with their implementation here on their example page:
http://ie.microsoft.com/testdrive/Graphics/VideoCaptions/Default.html

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