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Re: video use-case

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Mon, 6 Oct 2008 20:01:47 +1100
Message-ID: <2c0e02830810060201l26ebfe2n44c6bc8bb131d1d3@mail.gmail.com>
To: "Jack Jansen" <Jack.Jansen@cwi.nl>
Cc: "Media Fragment" <public-media-fragment@w3.org>

Hi Jack, all,


On Thu, Oct 2, 2008 at 7:55 AM, Jack Jansen <Jack.Jansen@cwi.nl> wrote:
> On 1-Oct-2008, at 17:42 , Pierre-Antoine Champin wrote:
>>>
>>> That would be the case for the use cases you explicitly mention here,
>>> but there are other multiplexed videos where this isn't the case, think
>>> of movies in airline  cut/normal cut/directors cut. This means that
>>> timestamps become messy: either "00h:02m:00s:00f" becomes ambiguous
>>> (could be different points depending on track selection), or arithmetic
>>> on timestamps becomes impossible (depending on track selection
>>> "00h:02m:00s:00f" may or may not be 60 seconds after "00h:01m:00s:00f".
>>
>> interesting example, indeed.
>> But, I would rather consider the different "cuts" to be different videos.

I regard them as different Web resources. The addressing of them is
always based on a specific Web resource just like different variants
of Web pages also live under totally different URLs and you can
address to them differently.


>> Indeed, the timeline is, in my view, a fundamental aspect of a video.
>
>
> Agreed.

Yes, I agree also - we are only dealing with one fixed timeline per resource.


> 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.
>
> Sylvia, do Annodex temporal URLs say anything about this?

Yes, Annodex proposes a sophisticated scheme for how to deal with this
situation.

As you can see from
http://annodex.net/TR/draft-pfeiffer-annodex-02.html#anchor14 the
Annodex resource that is returned upon a temporal URI request knows
whether it starts at an offset of 30s or not (stored in the
"presentationtime" header field).

http://annodex.net/TR/draft-pfeiffer-temporal-fragments-03.html#anchor6
describes the protocol aspect of it. If we ask for an offset of 30s we
have to expect the first frame to be at 30s and a 404 otherwise (in
the I-D an additional exception is mentioned for the case where the
server decides to dishonour the query and serve the resource without
the offset).


Cheers,
Silvia.
Received on Monday, 6 October 2008 09:02:24 GMT

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