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.html 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.

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 09:19:27 UTC