What does "UA rendered" mean? How does the UA render it? Can the UA just convert the format into WebVTT instead?
On Mon, Oct 13, 2014 at 11:15 AM, Bob Lund <b.l...@cablelabs.com> wrote: > > > On 10/12/14, 3:45 AM, "Silvia Pfeiffer" <silviapfeiff...@gmail.com> wrote: > > >Hi all, > > > >In the Inband Text Tracks Community Group we've recently had a > >discussion about a proposal by HbbTV. I'd like to bring it up here to > >get some opinions on how to resolve the issue. > > > >(The discussion thread is at > >http://lists.w3.org/Archives/Public/public-inbandtracks/2014Sep/0008.html > >, but let me summarize it here, because it's a bit spread out.) > > > >The proposed use case is as follows: > >* there are MPEG-2 files that have an audio, a video and several caption > >tracks > >* the caption tracks are not in WebVTT format but in formats that > >existing Digital TV receivers are already capable of decoding and > >displaying (e.g. CEA708, DVB-T, DVB-S, TTML) > >* there is no intention to standardize a TextTrackCue format for those > >other formats (statements are: there are too many formats to deal > >with, a set-top-box won't need access to cues) > > > >The request was to expose such caption tracks as textTracks: > >interface HTMLMediaElement : HTMLElement { > >... > > readonly attribute TextTrackList textTracks; > >... > >} > > > >Then, the TextTrack interface would list them as a kind="captions", > >but without any cues, since they're not exposed. This then allows > >turning the caption tracks on/off via JavaScript. However, for > >JavaScript it is indistinguishable from a text track that has no > >captions. So the suggestion was to introduce a new kind="UARendered". > > A clarification - the suggestion was for a new TextTrack.mode value of > ³UARendered² and for this type of TextTrack the only valid modes would be > ³UARendered² and ³disabled². The ³hidden² and ³showing² modes would not be > allowed since no Cues are generated. @kind would continue to denote the > type of TextTrack. > > Bob > > > > > >My suggestion was to instead treat such tracks as burnt-in video > >tracks (by combination with the main video track): > >interface HTMLMediaElement : HTMLElement { > >... > > > >readonly attribute VideoTrackList videoTracks; > >... > >} > > > >Using the VideoTrack interface it would list them as a kind="captions" > >and would thus also be able to be activated by JavaScript. The > >downside would that if you have N video tracks and m caption tracks in > >the media file, you'd have to expose NxM videoTracks in the interface. > > > > > >So, given this, should we introduce a kind="UARendered" or expose such > >tracks a videoTracks or is there another solution that we're > >overlooking? > > > >Silvia. > >
