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Re: Temporal fragments of media with time stamps

From: David Singer <singer@apple.com>
Date: Tue, 19 Jan 2010 16:48:06 +0900
Cc: "'Bailer, Werner'" <werner.bailer@joanneum.at>, public-media-fragment@w3.org, 'Richard Wright-ARCHIVES' <richard.wright@bbc.co.uk>, 'Jack Jansen' <Jack.Jansen@cwi.nl>
Message-Id: <3FAD8DC2-195C-4322-A896-696A28A9DE35@apple.com>
To: Davy Van Deursen <davy.vandeursen@ugent.be>
SMPTE time-codes are actually embedded in the media.  They might be continuous in a media file, they might not be.

For example, a fragment request for SMPTE 0h-10m-0s to 0h-20m-0s might appear to be a 10 minute clip starting 20 minutes in, but 
a) if the first time code in the file is in fact 0h-5m-0s, it's only 15 minutes into the clip (and indeed, TV time-codes typically treat 10h as the start time, I have no idea why)
b) if there is a discontinuity in the time-codes such that 0h-15m-59s is followed by 0h-18m-0s, then it's only an 8 minute cli[p that's requested, in fact.

On Jan 19, 2010, at 16:23 , Davy Van Deursen wrote:

>> -----Original Message-----
>> From: public-media-fragment-request@w3.org [mailto:public-media-
>> fragment-request@w3.org] On Behalf Of David Singer
>> Sent: maandag 18 januari 2010 2:38
>> To: Jack Jansen
>> Cc: Davy Van Deursen; 'Bailer, Werner'; public-media-fragment@w3.org;
>> 'Richard Wright-ARCHIVES'
>> Subject: Re: Temporal fragments of media with time stamps
>> On Jan 18, 2010, at 8:06 , Jack Jansen wrote:
>>> On 16 jan 2010, at 10:25, Davy Van Deursen wrote:
>>>> Temporal fragments should indeed take into account embedded time
>> stamps.
>> 'may', I think, surely.  It depends on whether the fragment time is
>> expressed in NPT, or (say) SMPTE time-codes.  NPT starts at 0;  to
>> resolve a fragment here, you're fine without inspecting the media.
>> SMPTE time-codes, OTOH, need to be found.  They might not even be
>> continuous in the media.
> Hmm, what do you mean by 'need to be found'? Suppose an MP4 file starting
> with an empty edit of 20s, followed by 40s video. What is the meaning of
> t=npt:0,30 and t=smpte:00:00:00:00,00:00:30:00? IMO, they will both result
> in an MP4 file starting with an empty edit of 20s, followed by 10s, no?
> Best regards,
> Davy
> -- 
> Davy Van Deursen
> Ghent University - IBBT
> Department of Electronics and Information Systems - Multimedia Lab
> URL: http://multimedialab.elis.ugent.be/dvdeurse

David Singer
Multimedia and Software Standards, Apple Inc.
Received on Tuesday, 19 January 2010 07:48:41 UTC

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