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Checking Quicktime

From: Michael Cooper <mcooper@cast.org>
Date: Sun, 20 Feb 2000 19:10:22 -0500
To: <w3c-wai-er-ig@w3.org>
Message-ID: <NCBBJOMIELMIDGCAPFCIGEFECPAA.mcooper@cast.org>
I was asked to evaluate what we could check for in Quicktime if we were
going to read the file. I'm no expert in the area so I hope I represent the
documentation right. Pretty much what we're interested in is the presence of
tracks that serve as alternatives to others, especially text tracks. Here's
what I get:

A track can be a video, sound or text track, or one of a number of other
formats that are part of the internal processing. A track can have a
reference to another track. This reference can indicate, among other things,
that the source track is _synchronized_ with the target track, or that it
serves is a _transcript_ of the target track. We're likely to find sound and
video tracks synchronized, but we could also find a text track synchronized
(with the video and/or sound tracks) and would look for that.

A possible alternate way to determine synchronization (and I suspect more
often found) is if two tracks both refer to the same _time code track_, I
think that means they're implicitly synchronized. I'm also inclined to guess
that the simple fact of a text track referencing a time code track would
indicate that the text track is presented in synchrony with something, or at
any rate isn't a copyright statement which probably wouldn't have time codes
or display properties. We can look for the presence of display properties
for a text track, but I think even a copyright statement might have those so
I wouldn't suggest that be part of the algorithm.

An implementor is going to have to go much deeper than this, but maybe this
lets us know what we can/can't suggest.

Michael

Michael Cooper
Bobby Project Manager
Technical Designer
CAST, Inc.
39 Cross St.
Peabody, MA  01960
Tel +1 978-531-8555 x265
TTY +1 978-538-3110
Fax +1 978-531-0192
Email mcooper@cast.org
http://www.cast.org/
http://www.cast.org/bobby/
Received on Sunday, 20 February 2000 19:13:03 GMT

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