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RE: Why use time as a unit of measurement? (was: Proposal 0.0)

From: Dave Singer <singer@apple.com>
Date: Wed, 12 Feb 2003 14:18:41 -0800
Message-Id: <p05200e03ba70781acd44@[10.169.91.126]>
To: Johnb@screen.subtitling.com, lists@wiltgen.net, public-tt@w3.org

>  > > I can conceive of other situations where the assumption of 1 sec per sec
>is invalid.
>
>>  I know you're not serious, but I don't get the joke.
>
>Well it wasn't exactly a joke. The point was that if you use a duration
>based mechanism, and you wish to support slow play or reverse play (or
>random access), then you invoke a large number of conversions from the
>duration based representation into an absolute time representation. If you
>start with an absolute time representation - then all that is necessary for
>reverse play or slow play is to alter the rate (or value) of your (internal)
>clock. Duration based mechanisms buy you nothing - and cost you lots.

On the contrary.  Given a document with relative durations, inserting 
or deleting a segment is easy;  everything naturally moves up and 
down when you do that.  If the document uses absolute values, rather 
than relative, this is painful.

One of the simplest uses is a timed-text file with relative 
durations, displaying (for example) captions, layed into a SMIL 
presentation in 'par' with the video and in a separate region.  This 
ought to work...

I don't disagree that perhaps SMIL needs some concept of how to align 
time-codes in two 'par' media, but that is a composition question 
that ought to be addressed in SMIL.


-- 
David Singer
Apple Computer/QuickTime
Received on Wednesday, 12 February 2003 17:22:57 GMT

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