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

From: Glenn A. Adams <glenn@xfsi.com>
Date: Tue, 18 Feb 2003 16:11:48 -0500
Message-ID: <7249D02C4D2DFD4D80F2E040E8CAF37C01FBCB@longxuyen.xfsi.com>
To: "Cyril Concolato" <cyril.concolato@enst.fr>, "John Glauert" <J.Glauert@sys.uea.ac.uk>
Cc: <Johnb@screen.subtitling.com>, <singer@apple.com>, <public-tt@w3.org>

As an FYI, SMIL 2.0 already supports what you describe below via
the syncMaster attribute. For example,

  <video src="..." syncBehavior="locked" syncMaster="true"/>
  <audio src="..." syncBehavior="locked"/>
  <textstream src="..." syncBehavior="locked" syncTolerance="0.5s"/>

In this example, the video media serves as the sync master, while
the audio and text streams are locked to the video. The text stream
may slip up to +/- 0.5s from sync without resync.


> -----Original Message-----
> From: Cyril Concolato [mailto:cyril.concolato@enst.fr] 
> Sent: Tuesday, February 18, 2003 8:13 AM
> To: John Glauert
> Cc: Johnb@screen.subtitling.com; singer@apple.com; public-tt@w3.org
> Subject: Re: Why use time as a unit of measurement? (was: 
> Proposal 0.0)
> Dear John, all,
> > A new par-like construct could be designed where the second stream 
> > (TT) is locked to the first (video). The video can be stopped, 
> > started, rewound, played at variable speed, have ads inserted, etc. 
> > The corresponding parts of the TT stream are displayed in 
> sync (cued 
> > in and cued out as required).
> >
> > This could probably be seen as syntactic sugar for "pure" SMIL, but 
> > would be much more compact since all the triggering is implicit. 
> This behavior very much ressembles to the OCR dependency in MPEG-4.
> For those who may not know MPEG-4 very well, let me explain 
> this notion 
> a little bit more in details. Within MPEG-4 Systems, you have 
> the Binary 
> Format for Scenes (BIFS) which is a binary format to describe the 
> spatial and temporal layout of the presentation as well as the media 
> that compose the presentation (Audio, Video, 2D/3D Graphics 
> and Text). 
> The synchronization is not described within the BIFS description. For 
> that purpose, you have the Object Description Framework (ODF) 
> which by 
> the means of an Object Descriptor (OD) describes, among other things, 
> the synchronisation properties of a media. Hence, in the OD, you can 
> specify that the clock reference of a media stream is the clock of 
> another stream. Therefore, when the user clicks on the video 
> to start, 
> stop or pause it, the other stream is automatically started, 
> stopped or 
> paused. In your case, the clock reference of the TT stream is 
> the clock 
> of the video stream.
> To map this into a SMIL-like notion, I would rather see this 
> notion be 
> put in the header section of the document than in a par element.
> Since a stream can depend only on one clock, you don't want to 
> manipulate this at the par element level but instead declare 
> it once for 
> the whole presentation (document).
> Best Regards,
> Cyril Concolato
> -- 
> Ecole Nationale Supérieure des Télécommunications, Paris
> Dept. Comelec
> 46, rue Barrault 75013 Paris                
> Tel: +33145817991    Fax: +33145804036
Received on Tuesday, 18 February 2003 16:11:51 UTC

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