TTML support

[sirkro]

In the latest release of DashJS (1.4.0), they added support for TTML.

It would be perfect if support for TTML could be added to Shaka-player.

Teststream: http://dash.edgesuite.net/dash264/TestCases/4b/qualcomm/1/ED_OnDemand_5SecSeg_Subtitles.mpd

<AdaptationSet mimeType="application/ttml+xml" lang="en">
      <Role schemeIdUri="urn:mpeg:dash:role" value="subtitle" />
      <Representation id="7"  bandwidth="268" >
        <BaseURL>English_track.xml</BaseURL>
      </Representation>
    </AdaptationSet>
      <AdaptationSet mimeType="application/ttml+xml" lang="ge">
      <Role schemeIdUri="urn:mpeg:dash:role" value="subtitle" />
      <Representation id="8"  bandwidth="268" >
        <BaseURL>German_track.xml</BaseURL>
      </Representation>
    </AdaptationSet>

[joeyparrish]

Thanks for the request. At the moment, we rely on the browser's subtitle support. On Chrome or Firefox, Shaka Player will do WebVTT.

For context, Shaka Player has made a point of not doing any DOM manipulation or CSS so far. Both of those things would have to change in order for us to render any subtitle format not directly supported by the browser. It's doable, but would require some architectural changes first.

We can't fit this into our schedule right now, but we'll keep it in mind.

[sanbornhilland]

Related to this and a possible alternative for some people, how difficult would it be to add an option to sidecar load WebVTT subtitles?

[tdrews]

Please see #133 for a separate discussion on sidecar loading (outside of the MPD) WebVTT subtitles.