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[Bug 14104] Video: Streaming text support in track element

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Date: Thu, 15 Sep 2011 01:07:32 +0000
To: public-html-bugzilla@w3.org
Message-Id: <E1R40QO-0001ZZ-Ln@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=14104

--- Comment #2 from Ralph Giles <giles@mozilla.com> 2011-09-15 01:07:31 UTC ---
Playback is generally happening inside the context of a media element, so we
would compare the timestamps on the cues against the currentTime attribute of
that media element to determine which are active.

The way I envisioned this working is that a <track> elements points to a src
url handled by a server which holds the connection open, sending new WebVTT
cues as they become available. The media element would then make a best effort
to display those cues at the appropriate time.

There is certainly an issue with knowing whether you have the next cue or not.
The current spec addresses this by requiring that the entire caption file be
loaded before playback can begin. While one can certainly implement the live
case with XHR and mutable text tracks, I think it is preferable to allow live
streaming of captions with just the <track> element.

The user agent does know when it has the next cue in the stream, so one
possible solution is to trigger ready state on that. Or we could leave it to
best effort in the live case and see how it works.

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Received on Thursday, 15 September 2011 01:07:34 UTC

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