[whatwg] Comments about the track element

Cyril Concolato cyril.concolato at telecom-paristech.fr
Wed Jul 25 05:44:58 PDT 2012

Le 7/24/2012 5:04 PM, Ian Hickson a écrit :
> [only replied on the whatwg list; please if possible avoid cross-posting
> as it tends to fracture threads when people only on one list and not the
> other reply]
[I'll forward the mails to the SVG mailing list separately to make sure 
people not subscribed to the whatwg list can still get the whole discussion]
> On Tue, 24 Jul 2012, Cyril Concolato wrote:
>> During the ongoing SVG F2F meeting, the SVG WG discussed the use case of
>> displaying SVG graphics on top of a video, in a synchronous manner.
>> The SVG WG believes that for such use case, it is necessary to indicate
>> to the browser that the SVG and video content should stay synchronized
>> (no matter what happens to the video playback), and to let the browser
>> handle the synchronization internally. The SVG WG resolved to include
>> such indication as part of the Web Animation specification, for instance
>> using the HTML mediagroup attribute or the MediaController API.
>> However, the SVG WG thinks it would also be interesting to leverage the
>> native UI controls of the video element to select (or deactivate) the
>> display of the SVG content on top of the video, in a similar manner to a
>> subtitle track. Obviously, the HTML 5 track element would be a suitable
>> option for that. However, currently it only allows text tracks. So, the
>> SVG WG would like HTML to allow the track element's URL to identify an
>> SVG resource, and in that case the track kind would be 'graphics'. There
>> would be a need to define how the graphics are displayed on top of the
>> video, for instance reusing the viewport/viewbox negotiation phase.
>> There would also be a need to make a more generic Track API or to
>> replace the TextTrack API by the SVG API when the track is of kind
>> 'graphics'.
> My understanding is that the expected way to solve this previously was
> using SMIL, putting the video in the SVG itself. That seems to make more
> sense that having the SVG layered on top of an HTML video. Why is this no
> longer a viable solution?
First, the SVG WG resolved to align the SVG audio and video element with 
the HTML 5 ones.
Then, in any case, I think both options are reasonable and viable. If 
your application is primarily SVG, you can indeed use a video element in 
SVG. But if your application is mainly HTML, and you just want to 
display SVG on top of the video, it makes perfect sense to stay in HTML 
I think.


Cyril Concolato
Maître de Conférences/Associate Professor
Groupe Multimedia/Multimedia Group
Telecom ParisTech
46 rue Barrault
75 013 Paris, France

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