W3C home > Mailing lists > Public > public-media-fragment@w3.org > October 2008

Re: video use-case

From: Yannick Prié <yannick.prie@liris.cnrs.fr>
Date: Mon, 6 Oct 2008 14:11:56 +0200
Cc: "Jack Jansen" <Jack.Jansen@cwi.nl>, "Media Fragment" <public-media-fragment@w3.org>
Message-Id: <A4A5AAD4-7285-4A62-A43B-D378537D1C17@liris.cnrs.fr>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>

Hi Silvia

>>> Agreed. But this triggered another question: are we interested in  
>>> the
>>> timestamps in the movie? If we ask for a segment of video starting  
>>> at 30s,
>>> do we expect the timestamp of the first frame to be "30s"? Do we  
>>> expect it
>>> to be "0s"? Do we expect nothing at all? This is going to be  
>>> important for
>>> client-side creation of URLs for selecting subparts of videos.
>> I can consider a fragment of a video as a video, and I do not care  
>> about the
>> architecture that allows me to see it, download it, etc. as a  
>> video. It
>> begins at 0s.
> Actually, if I request a video from 30sec offset, I expect it to start
> at 30sec. Otherwise I will be confused and wonder whether the offset
> has actually worked. If I download it, the video may have forgotten
> that it was originally started at 30sec offset (this is particularly
> the case where the video format does not offer storage of an offset).
> In that case (i.e. an offline video player) it's probably ok to run it
> with a 0sec offset, even though it's generally wrong.
>> I can consider a fragment of a video as a fragment of a video. In  
>> that case
>> it begins at 30s, I can explicitly manipulate both the fragment and  
>> the
>> video (e.g. jump to a frame before the fragment beginning, let's  
>> say at
>> 20s).
>> I think both cases should be considered. I do not manipulate a  
>> "video" and a
>> "fragment of a video" in the same way, even if their playing can  
>> result in
>> the same rendering (eg. 5 seconds of video in a web page).
> I'm curious: how would you manipulate a "video" and a "fragment of a
> video" differently? Can you explain?

Well, I just insisted on the fact that from an applicative point of  
view, a "video" is different from a "video fragment", it is the  
difference between, let's say
- considering a shot of a video as a plain video by itself (not  
explicitly knowing it is actually a fragment of another video, or  
generated on the fly, or anything else): all I know about it are its  
video characteristics, all I can do is play it as a video and related  
- and considering a shot of a video as a fragment of a specific video:  
I know it from its fragment characteristics, ie I know the video it is  
extracted from as a video, and I know the fragment as such. It enables  
me for instance to play the fragment while giving access to the plain  
video it is a fragment of.

The notion of "fragment in context" and "fragment out of context"  
seems to be a good expression of such difference, though the question  
is whether I could even forget about the fragment being a fragment  
(from my applicative point of view).

It is possible to say that it is no problem, because users will always  
manipulate video through dedicated user interfaces that can hide /  
manage such differences, or to consider that URI and related  
mechanisms proposed by the group should be made sufficiently clear so  
as to offer direct manipulation inside textual webpages definitions,  
and somehow reflect these differences.



Yannick Prié - MCF Informatique - LIRIS UMR 5205 CNRS
UFR Informatique - Université Lyon 1 - F-69622 Villeurbanne Cedex
Tél: (+33) 4 72 43 16 36 Mél: yprie@liris.univ-lyon1.fr
Fax: (+33) 4 72 43 15 36 Web: http://liris.cnrs.fr/~yprie
Received on Monday, 6 October 2008 12:24:46 UTC

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