[Bug 22785] there should be a way to schedule audio/video track selection changes in HTMLMediaElements

https://www.w3.org/Bugs/Public/show_bug.cgi?id=22785

--- Comment #17 from Michael Thornburgh <mthornbu@adobe.com> ---
(In reply to comment #15)
[...]> 
> I think given the work on Web Animations, we may not even need need the use
> of a WebVTT track to pre-schedule transitions between different video tracks
> - Web Animations should be capable of providing that functionality:
> http://dev.w3.org/fxtf/web-animations/ together with the use of track
> fragments to specify which track to switch to:
> http://www.w3.org/TR/2011/CR-media-frags-20111201/#naming-track .

from my initial reading of Web Animations, this approach on first glance seems
appealing, if one could animate a track element's enabled/selected attribute
from false to true at a particular time, and if the HTMLMediaElement's play
timeline could be the animation timeline/clock.

it didn't seem like the enabled/selected attribute would be among the class of
"animate-able" attributes.  if you needed a timed event, then you're back to
the "JavaScript driving track changes" problem.

i think the timing model of Web Animations, specifically of the time being
sampled and items animating instantaneously according to the (transformed) time
at that instant, won't work for seamless track switches, because in order to
effect a seamless transition during playback the media engine will have had to
buffer up data from the to-be-selected tracks and begun decoding ahead of the
switch.  as Aaron pointed out earlier, the media engine may need to know
significantly ahead of time (he stated 20-500ms) to effect a seamless
transition.

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Received on Thursday, 8 August 2013 23:55:47 UTC