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Re: ISSUE-1: Combining Media Fragment URI with other time-clipping methods

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Tue, 27 Jan 2009 23:33:31 +1100
Message-ID: <2c0e02830901270433t5af6024cv481de26e7f3d43e6@mail.gmail.com>
To: RaphaŽl Troncy <Raphael.Troncy@cwi.nl>
Cc: Media Fragment <public-media-fragment@w3.org>

On Tue, Jan 27, 2009 at 11:18 PM, RaphaŽl Troncy <Raphael.Troncy@cwi.nl> wrote:
>
> ISSUE-1: Combining Media Fragment URI with other time-clipping methods
>
> http://www.w3.org/2008/WebVideo/Fragments/tracker/issues/1
> Raised by: RaphŽl Troncy
>
> Related to ACTION-13 [1] closed by Jack, see the whole thread starting at
> [2], I raise this issue since everything is not crystal clear for me.
>
> I assume that the media fragment is regarded as in-context, that is,
> http://www.example.com/video.mov#t=20,30 will play the fragment between the
> seconds 20 and 30 of this resource, but the user sees the whole timeline of
> the video and can click elsewhere on the slider, thus making a new request.
>
> I understand that specifying a time-clipping method, for example in SMIL, is
> relative to the (timeline of the) resource. Therefore, what's happened if I
> have:
> <video clipBegin="5s" clipEnd="15s"
> src="http://www.example.com/video.mov#t=20,30"/> ?
>
> Scenario 1: the media fragment is completely ignored, the UA plays the video
> segment between the seconds 5 and 15
>
> Scenario 2: the clipping method is done relatively to the media fragment,
> the UA plays the video segment between the seconds 25 (=20+5) and 35
> (=20+15)
>
> Scenario 3: the clipping method is done relatively to the media fragment but
> bound to the media fragment, the UA plays the video segment between the
> seconds 25 (=max[20,20+5]) and 30 (=min[30,20+15]).
>
> In summary, how do we cover the cases where the media fragment is i)
> encompassing, ii) embedding, iii) disjoint and iv) partially overlapping the
> boundaries of the other time-clipping method?
>
> [1] http://www.w3.org/2008/WebVideo/Fragments/tracker/actions/13
> [2]
> http://lists.w3.org/Archives/Public/public-media-fragment/2008Nov/0095.html
>

>From my viewpoint, the URL points to a resource. Thus scenario 3 is
the correct one, because from a SMIL POV, the clipBegin and clipEnd
attributes are calculated on the resource.

BTW: the HTML5 video element has dropped the clipBegin and clipEnd
elements for this reason and is leaving all time clipping to be done
through fragment addressing, i.e. us. We have to make sure we
understand when to have a full resource available, when to treat it as
a part of a resource with a context (and therefore a longer timeline),
and when to treat it as a file fragment that is not even a playable
file (but required for buffering in the browser).

Cheers,
Silvia.
Received on Tuesday, 27 January 2009 12:34:08 GMT

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