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

From: <bugzilla@jessica.w3.org>
Date: Sat, 29 Oct 2011 08:56:30 +0000
To: public-html-bugzilla@w3.org
Message-Id: <E1RK4iM-0007hL-Gu@jessica.w3.org>
http://www.w3.org/Bugs/Public/show_bug.cgi?id=14104

--- Comment #13 from Silvia Pfeiffer <silviapfeiffer1@gmail.com> 2011-10-29 08:56:28 UTC ---
(In reply to comment #12)
> Could you elaborate on those bullet points?

Sure.

The @secondsMissed attribute would be an attribute on the media element that
says how many seconds ago the stream had started, i.e. what time offset
currentTime=0 maps to. Given that the times in the WebVTT file would be
relative to that original start time, you can calculate when the cues would
need to be presented at by calculating currentTime + secondsMissed as the
video's playback time.

The reload mechanism on the <track> elements would mean that when the
currentSrc resource's last cue has been read and is before the end of the
video, while the video continues to load, do a HTTP byte range request for
bytes on the currentSrc resource after the end of the file. E.g. if the
currentSrc resource is 600KB long, then do a GET request with Range: bytes=600-
. This would be repeated while more video is being downloaded and stopped
otherwise. The repetition frequency would likely be attached to the request
rate of the video.


As for the change in WebVTT, the idea is that the following would be legal:

WEBVTT

00:00:00.000 --> next
This cue lasts until the next cue replaces it, i.e. 5.6 sec.

00:00:05.600 --> next
Same here, i.e. 4.4 sec.

00:00:10.000 --> next
If none follows, the cue lasts until the end of the video.


These three together would allow for live captioning through streaming text.

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Received on Saturday, 29 October 2011 08:56:36 UTC

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