RE: MPEG-2 TS Closed Caption mapping



> -----Original Message-----
> From: Silvia Pfeiffer [mailto:silviapfeiffer1@gmail.com]
> Sent: Wednesday, May 14, 2014 3:19 AM
> To: Ladd, Pat
> Cc: Clift, Graham; Bob Lund; public-inbandtracks@w3.org
> Subject: Re: MPEG-2 TS Closed Caption mapping
> 
> On Tue, May 13, 2014 at 7:13 AM, Ladd, Pat
> <Pat_Ladd2@cable.comcast.com> wrote:
> > Graham;
> >
> >     I took a different meaning from your question.  In
> http://rawgit.com/silviapfeiffer/HTMLSourcingInbandTracks/master/index.h

> tml section 3, the table in step 3 indicates that when a Caption Service
> Descriptor is signaled in a PMT a TextTrack is created with kind "captions" and
> in the case of captions digitized in the video stream, i.e. CEA708, the id is the
> PID of the video elementary stream carrying the captions.
> 
> Correct.
> 
> >  What I gather from that is setting the captions TextTrack mode to showing
> will cause the captions in the video stream to be rendered.
> 
> Incorrect. They can only be rendered by the browser if the browser
> understands the caption format. For example, WebM has captions in
> WebVTT format - they will be exposed as a TextTrack with VTTCue captions
> and thus follow the WebVTT rendering spec. If your captions come from a
> MPEG4 file in a CEA708 track, a TextTrack can be created, but the captions
> cannot be exposed in a renderable form, since there is no TextTrackCue
> format for CEA708.

If the captions are to be rendered ONLY by the UA then it would seem there is no need to define a cue format. It would be implementation dependent how the UA formats caption data for rendering.

> 
> I am currently looking at how to generically map such things to DataCue, or
> whether we should use a new MPEG-based Cue format that Bob has been
> designing. There'll be more on this soon.
> 
> Cheers,
> Silvia.
> 
> >
> > Pat...
> >
> > -----Original Message-----
> > From: Silvia Pfeiffer [mailto:silviapfeiffer1@gmail.com]
> > Sent: Sunday, May 11, 2014 12:52 PM
> > To: Clift, Graham; Bob Lund
> > Cc: public-inbandtracks@w3.org
> > Subject: Re: MPEG-2 TS Closed Caption mapping
> >
> > Hi Graham,
> >
> > audio and video tracks can be activated the same way that text tracks are,
> except there is no browser-provided default UI, so the JS developer has to
> do that.
> >
> > AudioTrack has 'enabled'
> > http://www.w3.org/html/wg/drafts/html/master/embedded-

> content.html#dom
> > -audiotrack-enabled
> > and
> > VideoTrack has 'selected'
> > http://www.w3.org/html/wg/drafts/html/master/embedded-

> content.html#dom
> > -videotrack-selected
> > .
> >
> > HTH.
> >
> > Also note that Bob has made a small change to the new spec and updated
> the caption selection part:
> > http://rawgit.com/silviapfeiffer/HTMLSourcingInbandTracks/master/index

> > .html
> >
> > Cheers,
> > Silvia.
> >
> >
> > On Sat, May 10, 2014 at 3:27 AM, Clift, Graham
> <Graham.Clift@am.sony.com> wrote:
> >> The ‘Sourcing In-band Media Resource Tracks from Media Containers into
> HTML’
> >> spec seems to imply that CC track description will either be
> >> presented to the application as a TextTrack when the captions are not
> >> line 21 or as Audio/Video track when they are line 21.
> >>
> >>
> >>
> >> So the question I had is, how does the application set line 21
> >> captions to showing when contained as an audio or video track?
> >>
> >>
> >>
> >> Regards
> >>
> >>
> >>
> >> Graham
> >

Received on Wednesday, 14 May 2014 13:27:03 UTC