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Re: video use-case

From: RaphaŽl Troncy <Raphael.Troncy@cwi.nl>
Date: Tue, 14 Oct 2008 14:07:25 +0200
Message-ID: <48F48B7D.7030801@cwi.nl>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
CC: Yves Lafon <ylafon@w3.org>, Jack Jansen <Jack.Jansen@cwi.nl>, Yannick Priť <yannick.prie@liris.cnrs.fr>, Media Fragment <public-media-fragment@w3.org>

Dear Silvia,

[...]

> The biggest problem here being that
> time is inherently inaccurate (for being essentially a floating point
> number) while bytes are accurate (for being an integer). So, if you
> are asking for times 1:23-1:45.32 and then 1:45.33-1:56 in two
> fragment requests, it is somewhat impossible for the Web proxy to know
> whether that is enough data to compose 1:23-1:56 or whether it has
> accidentally missed or duplicated a few dozen bytes because they fell
> into the gap between the two segments because the time resolution
> cannot be made completely accurate for media resources.

I (and others) did propose a while ago an internal representation of 
time using the least common multiple between the usual sound sample rate 
(96000 and sub-multiple or 44100 and sub-multiple) and video frame rate 
(30, 25, 24), that is 14112000. This integer defines then an universal 
common sample rate (i.e. 14112000 corresponds to 1 second) and any 
temporal point in an audio-visual content will be represented as an 
integer on this temporal basis. You can see the details in the paper:

RaphaŽl Troncy, Jean Carrive, Steffen Lalande and Jean-Philippe Poli.
"A Motivating Scenario for Designing an Extensible Audio-Visual 
Description Language". In International Workshop on Multidisciplinary 
Image, Video, and Audio Retrieval and Mining (CoRIMedia), Sherbrooke, 
Canada, October 25-26, 2004.
http://www.cwi.nl/~troncy/Publications/Troncy-corimedia04.pdf

Does that help to solve the problem?
Cheers.

   RaphaŽl

-- 
RaphaŽl Troncy
CWI (Centre for Mathematics and Computer Science),
Kruislaan 413, 1098 SJ Amsterdam, The Netherlands
e-mail: raphael.troncy@cwi.nl & raphael.troncy@gmail.com
Tel: +31 (0)20 - 592 4093
Fax: +31 (0)20 - 592 4312
Web: http://www.cwi.nl/~troncy/
Received on Tuesday, 14 October 2008 12:08:15 GMT

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