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Re: Behaviour of Smart UAs vs. UAs that need server help in error cases

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Tue, 3 May 2011 21:28:54 +1000
Message-ID: <BANLkTikhAvNqhZaiRpLfTL7B0haszZH2RQ@mail.gmail.com>
To: Davy Van Deursen <davy.vandeursen@ugent.be>
Cc: Media Fragment <public-media-fragment@w3.org>
On Tue, May 3, 2011 at 9:12 PM, Davy Van Deursen
<davy.vandeursen@ugent.be> wrote:
> Dear all,
>
> another topic related to the test case discussions ...
>
> The issue is about the case where we have an invalid media fragment URI, but
> that invalidity is only detectable by the UA if it has information regarding
> the source media (see [1] in the spec). For example: media.webm#t=15 and the
> duration of media.webm is only 10s.
>
> Suppose we have a smart UA (i.e., scenario described in [2], only byte range
> requests are used). The smart UA is able to determine the duration of the
> media, interprets the media fragment URI, and seeks to the end of the media
> (as discussed in [3]).
>
> So far so good, but what happens when we have a UA using a media
> fragments-enabled server (i.e., scenario described in [4], where time ranges
> are used)? The UA does not know the duration of the source media. Therefore,
> it just sends an HTTP Range request to the server:
>
> GET media.webm HTTP/1.1
> Range: t:npt=15-
>
> Since the requested time range is invalid, the server answers with a 416
> (Requested Range Not Satisfiable), and the UA still doesn't have a clue
> about the duration of the media.


An intelligent server should inform the UA with every request about
the content duration, even if it is an error, shouldn't it?

Silvia.

> So the question is, what is the behaviour of a UA getting a 416 from a Media
> Fragments-enabled server (especially in the case when the decoding pipeline
> is not setup)?
>
> I think this situation must be clarified in the spec.
>
> Best regards,
>
> Davy
>
> [1]
> http://www.w3.org/2008/WebVideo/Fragments/WD-media-fragments-spec/#error-media
> [2]
> http://www.w3.org/2008/WebVideo/Fragments/WD-media-fragments-spec/#processing-protocol-UA-mapped
> [3]
> http://lists.w3.org/Archives/Public/public-media-fragment/2011Apr/0054.html
> [4]
> http://www.w3.org/2008/WebVideo/Fragments/WD-media-fragments-spec/#processing-protocol-Server-mapped
>
> --
> Davy Van Deursen
>
> Ghent University - IBBT
> Department of Electronics and Information Systems - Multimedia Lab
> URL: http://multimedialab.elis.ugent.be/dvdeurse
>
>
Received on Tuesday, 3 May 2011 11:29:41 UTC

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