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

[bugzilla-daemon at webkit.org]

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





--- Comment #13 from Glenn Adams <glenn at skynav.com>  2013-02-21 19:45:56 PST ---
(In reply to comment #12)
> (In reply to comment #10)
> > (In reply to comment #9)
> > > I fail to understand how you can represent TTML in the browser without making use of these constructs that <track> stands for.
> > 
> > Where did I see I wouldn't make use of these constructs?
> 
> When you said:
> 
> > > > 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
> 
> 
> > Nothing here requires populating cues. That is, the set of cues could be exposed or not via the DOM.
> 
> Are you suggesting to parse a <track> element into a HTMLTrackElement, but not actually giving it a TextTrack object?

No. I'm saying that it isn't necessary to populate the cue list.

> 
> Are you further suggesting to "just render" the text on top of the video without adding it to the shadow DOM?

I'm not exactly sure what you are referring to as shadow DOM here, but if you are referring to TextTrack, then there is no reason not to provide a TextTrack object. But individual cues aren't needed in TextTrack to  perform formatting of TTML content.

> How is this rendering supposed to work? Are you intending to render pixels into the video before the video is displayed?

I'm assuming there is a reasonable implementation specific way to overlay a graphics layer over a video layer in WK's display pipeline. Since WebVTT is displaying over video, then clearly there is some functionality there to support this.

> The way in which <track> is specified in HTML5 is that it introduces content into the browser that a JS developer can manipulate. Therefore it populates all of the objects. This is intentional and not a bug.

Sure. But there is nothing in the HTML5 spec that says that cues (or what might be considered a "cue") *must* be exposed and can't be implicitly presented or otherwise processed without exposing actual cue objects. At least there is nothing I'm aware of that mandates this. Please correct me if I've missed it.

One could also take a less minimalist approach (to exposing no cues) and populate cue objects that have nothing more than start/end times. My interpretation of UA behavior w.r.t. text tracks is that it is up to the UA and the specific track content type to define one or more mappings, one of which may be the empty set in terms of exposed cue objects.

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