Re: Captioning for live video

Hi Silvia,

Le 12/15/2012 12:14 PM, Silvia Pfeiffer a écrit :
> Hi Cyril,
>
> On Fri, Dec 14, 2012 at 10:03 PM, Cyril Concolato 
> <cyril.concolato@telecom-paristech.fr 
> <mailto:cyril.concolato@telecom-paristech.fr>> wrote:
>
>     Hi Silvia,
>
>>             2. Solution in WebVTT
>>
>>
>>         Separately from WebVTT syntax issues, currently the spec does
>>         not support streaming of WebVTT in <track>.
>>
>>
>>     That's what https://www.w3.org/Bugs/Public/show_bug.cgi?id=18029
>>     is about. I continue to believe that similarly to how we can
>>     stream a video live to a <video> element, we should be able to
>>     stream text to a <track> element and synchronize it from the cue
>>     time stamps.
>     I fully agree with that. In this respect, you might be interested
>     by the demo I made at MPEG back in October, showing synchronized
>     playback of streamed subtitles and video in a live scenario using
>     DASH. Details are here:
>     http://concolato.wp.mines-telecom.fr/2012/12/14/live-streaming-of-video-and-subtitles-using-dash/
>
>
> Ah this is very interesting.
>
> I wasn't able to find this by reading your slides and the link to the 
> demo goes to a file on C:// : did you use JavaScript and TextTrack to 
> feed WebVTT cues to the browser for rendering?
The demo indeed used C:// as this was using the meeting's network which 
was not so good and also because it's hard to let a live server run 
permanently on our university servers. I'm working on that to try and 
make the demo available online.

Yes, to feed the WebVTT cues, I followed a suggestion from Philip 
Jägenstedt [1]. I have a dummy HTML video element used to load the 
WebVTT segment and when it's loaded, I transfer the cues in JavaScript 
to the real video element. I would have preferred either a JavaScript 
function to parse the WebVTT segments or even better, support for WebVTT 
in Google's MSE implementation. Apparently, one way to do that would be 
embed WebVTT in MP4 or WebM, but that's a bit awkward I think.

HTH,
Cyril


[1] 
http://lists.w3.org/Archives/Public/public-whatwg-archive/2012Sep/0373.html

-- 
Cyril Concolato
Maître de Conférences/Associate Professor
Groupe Multimedia/Multimedia Group
Telecom ParisTech
46 rue Barrault
75 013 Paris, France
http://concolato.wp.mines-telecom.fr/