[whatwg] media resources: addressing media fragments through URIs spec

[Silvia Pfeiffer]

Hi Jonas,

On Thu, Jul 1, 2010 at 4:41 AM, Jonas Sicking <jonas at sicking.cc> wrote:
> Hi Silvia,
>
> Back in may last year I brought [1] up the fact that there are two use
> cases for temporal media fragments:
>
> 1. Skipping to a particular point in a longer resource, such as
> wanting to start a video at a particular point while still allowing
> seeking in the entire resource. This is currently supported by for
> example YouTube [2]. It is also the model used for web pages where
> including a fragment identifier only scrolls to a particular point,
> while allowing the user to scroll to any point both before and after
> the identified fragment.
>
> 2. Only displaying part of a video. For example out of a longer video
> from a discussion panel, only displaying the part where a specific
> topic is discussed.
>
> While there seemed to be agreement [3][4] that these are in fact two
> separate use cases, it seems like the media fragments draft is only
> attempting to address one. Additionally, it only addresses the one
> that has the least precedence as far as current technologies on the
> web goes.
>
> Was this an intentional omission? Is it planned to solve use case 1
> above in a future revision?
>
> [1] http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-May/019596.html
> [2] http://www.youtube.com/watch?v=fyQrKvc7_NU#t=201
> [3] http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-May/019718.html
> [4] http://lists.whatwg.org/htdig.cgi/whatwg-whatwg.org/2009-May/019721.html


I think you may have misunderstood the specification. Use case 1 is
indeed the main use case being addressed in the specification. There
is a Firefox plugin implementation[1] of the specification that shows
exactly use case 1 in a video element - a URI with a fragment such as
video.ogv#t=40,50 is being included in a <video> element and the
effect is that the video is displayed from 40s to 50s, but the
transport bar (or controls) are still those of the complete resource,
so you can still seek to any position.

To be sure, this is just a recommendation of how it is supposed to be
implemented (see
http://www.w3.org/TR/media-frags/#media-fragment-display). The group
only defined what URIs look like that point to such a segment - it
cannot prescribe what an application (such as a HTML document) does
with the URI. I would propose that this discussion should be had about
HTML5 and a sentence be added to the HTML5 spec on how UAs are
expected to deal with such segments.

Further, if you are indeed only interested in a subpart of the
original media resource and want to completely blend out all context
(i.e. all other bits of the media resource), you should be using the
URI query addressing method instead of the URI fragment, e.g.
video.ogv?t=40,50. This URI is supposed to create a new resource that
consist only of the segment - it will only do so, of course, if your
server supports this functionality.

All of this is described in more detail in the spec [2]. If that is
unclear or anything is confusing, please do point it out so it can be
fixed.

Best Regards,
Silvia.



[1] http://www.w3.org/2008/WebVideo/Fragments/code/plugin/ (expect some bugs)
[2] http://www.w3.org/TR/media-frags/