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

[bugzilla-daemon at webkit.org]

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





--- Comment #7 from Silvia Pfeiffer <silviapf at chromium.org>  2013-02-21 15:23:34 PST ---
(In reply to comment #6)
> (In reply to comment #5)
> I guess you are asking if I could provide a reference to rules for TTML that are equivalent to the following found in 10.4.1 Embedded content:

Yes.

> Is that what you are asking? At present, TTML leaves the decision about where to display the "root container region" up to the external authoring or presentation context (see [1], with a minor clarifying edit "[or presentation]"):
> 
> <quote>
> If the tts:extent attribute is specified on the tt element, then it must adhere to 8.2.7 tts:extent, in which case it specifies the spatial extent of the root container region in which content regions are located and presented. If no tts:extent attribute is specified, then the spatial extent of the root container region is considered to be determined by the external authoring or presentation context. The root container origin is determined by the external authoring [or presentation] context.
> </quote>

No, this is not sufficient. You actually need to explain how you are rendering the information found in a TTML file. This is not something that is part of the TTML format specification, but more like a mapping layer between the file format and the browser.


> So the language you cite in HTML5 10.4.1 can certainly apply as the "external presentation context" rules.

It's not just about what the "root container" means, but what everything in TTML is mapped to in HTML.

See for example http://dev.w3.org/html5/webvtt/#webvtt-cue-text-dom-construction-rules to see how the tags and elements used in WebVTT are mapped to HTML tags. This is something that is not clear in TTML. You need to explain what a TTML <p> element maps to and any other elements in use. You need to explain how to populate TextTrackCues.

You need to explain how to get to the CSS styling, see for example http://dev.w3.org/html5/webvtt/#webvtt-cue-text-rendering-rules . What CSS does an XSL-FO rule create in the HTML DOM?

It's impossible to implement the full scope of TTML without these clarifications. And it's impossible to implement it compatibly between browsers without a specification for it.

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