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.
