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

[bugzilla-daemon at webkit.org]

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





--- Comment #3 from Maciej Stachowiak <mjs at apple.com>  2013-02-21 10:38:13 PST ---
(In reply to comment #2)
> (In reply to comment #1)
> > If anyone plans to work on this, don't forget to follow this process: <http://www.webkit.org/coding/adding-features.html>.
> 
> Certainly. Also, I would expect any code to be bracketed with
> 
> #if ENABLE(VIDEO_TRACK) && ENABLE(TTML)
> #endif

You need consensus to add the feature even if it has a feature flag.

> 
> > I am not sure that the WebKit community will be interested in having an implementation of TTML, particularly given the dependency on the XSL-FO formatting model.
> 
> (1) the use of XSL-FO in the TTML spec is only for explanatory purposes, namely, describing formatting semantics, and not used for implementation purposes; the same semantics can be restated in terms of CSS as well; so that is not really a substantive objection;

I don't believe the full XSL-FO formatting model can be mapped CSS, or if it can, no one has done so; it may be possible for the subset of XSL-FO used by a subset of TTML.

> 
> (2) IE10 implements support for a subset of TTML;
> 
> (3) the FCC rules could translate to mandatory support in a variety of deployment contexts, e.g., HTML5 UAs embedded in television devices available at retail that are already subject to a variety of FCC rules;

There are many possible interpretations of the FCC rules. Some say that it's not necessary to specifically implement SMPTE-TT, the safe harbor format, as long as a format with all the mandated capabilities is supported. I have yet to hear an interpretation it's required to implement a subset of TTML that's not the same profile as SMPTE-TT.

I think you will find addition of this feature is controversial, as WebVTT exists in part because of some browser implementors objecting to the complexity of TTML.

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