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RE: TT and subtitling

From: <Johnb@screen.subtitling.com>
Date: Fri, 31 Jan 2003 17:34:30 -0000
Message-ID: <11E58A66B922D511AFB600A0244A722E6C5FD9@NTMAIL>
To: glenn@xfsi.com
Cc: public-tt@w3.org

I wrote:

> 	While for subtitling purposes a duration based approach solves
> certain problems, it does not solve all problems caused by interruption of
> the stream or change of intent. It is certainly preferable to an
> overwriting approach. 
	Glenn A. Adams wrote:

> 	Could you provide more detail of why overwriting is preferred? 
	I actually personally favour a duration based approach, however as I
alluded in my previous mail, an overwriting approach has some advantages if
you need to erase something before it's programmed expiration. A duration
based approach has the obvious characteristic of passing the timing
responsibility to the decoder. Teletext subtitling uses a combination of
combining and overwriting to achieve certain effects (Snake and Add on). DVB
also uses an overwriting approach. For Teletext it is reasonable to use
'push' techniques - as to require the TV decoder to time subtitles would be
an overcomplicated solution. However this is an pre-existing emission
context - and I can see how translation from TT to Teletext emission would
be feasible. For DVB the justification for overwriting is less clear.

	For TT in general I would favour a duration based approach - since
it fits better with a 'self contained access unit' philosophy - yet in a
streamed context the ability to instantly erase would be desirable.

	regards John Birch

The views and opinions expressed are the author's own and do not necessarily
reflect the views and opinions of the Screen Subtitling Systems Limited.
Received on Friday, 31 January 2003 12:36:53 UTC

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