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RE: Temporal fragments of media with time stamps

From: Davy Van Deursen <davy.vandeursen@ugent.be>
Date: Sat, 16 Jan 2010 10:25:08 +0100
To: "'Jack Jansen'" <Jack.Jansen@cwi.nl>, "'Bailer, Werner'" <werner.bailer@joanneum.at>
Cc: <public-media-fragment@w3.org>, "'Richard Wright-ARCHIVES'" <richard.wright@bbc.co.uk>
Message-ID: <003601ca968d$cc119560$6434c020$@vandeursen@ugent.be>
Werner, Jack,

> -----Original Message-----
> From: public-media-fragment-request@w3.org [mailto:public-media-
> fragment-request@w3.org] On Behalf Of Jack Jansen
> Sent: vrijdag 15 januari 2010 22:36
> To: Bailer, Werner
> Cc: public-media-fragment@w3.org; Richard Wright-ARCHIVES
> Subject: Re: Temporal fragments of media with time stamps
> 
> 
> On 15 jan 2010, at 16:56, Bailer, Werner wrote:
> 
> > Dear all,
> >
> > I had an email discussion with Richard Wright from the BBC, who
> brought up the following point: If media files have embedded time
> stamps (as it is possible e.g. in MPEG-2), temporal fragments should
> use them, instead of just using the offset from the start. This could
> for example make a difference when time stamps do not start at 0 at the
> beginning of the file or in case frames have been dropped during
> recording (i.e. the frame count from the start does not match any
> more).
> >
> > The current specification is not clear, as it does not state whether
> it considers embedded time stamps if present:
> >
> > - For the wall-clock time code I assume it does, otherwise it would
> have to get the date/time from some other source.
> > - For the normalized play time I would expect to always specify a
> time offset relative to the start of the file.
> > - For the SMPTE time codes, it could consider time stamps if present.
> >
> > Maybe you have already discussed that issue, then the specification
> should state how it is handled.
> 
> 
> We discussed this early in the process. This thread
> <http://lists.w3.org/Archives/Public/public-media-
> fragment/2008Oct/0003.html> has part of that discussion (even though
> the initial message was about something slightly different).
> 
> But: I can't remember whether we actually reached a decision about
> embedded timestamps. One of the ideas was indeed to follow a scheme
> like you suggest, but I seem to recall there were also people who
> weren't in favor...
> 
> Anyone's memory better than mine?

Temporal fragments should indeed take into account embedded time stamps.
Note that this is already stated in the specification [1].

Best regards,

Davy

[1] http://www.w3.org/TR/media-frags/#processing-overview-interpretation  

-- 
Davy Van Deursen

Ghent University - IBBT
Department of Electronics and Information Systems Multimedia Lab
URL: http://multimedialab.elis.ugent.be/dvdeurse
Received on Saturday, 16 January 2010 09:23:39 GMT

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