[whatwg] Start position of media resources

[Silvia Pfeiffer]

Hi Chris,

At the end of last year (I cannot find the thread any more) there was
a discussion about removing a start offset attribute from the video
element. The reason it was removed is that the W3C media fragments
working group is working on a specification that is similar to the
temporal URI specification that Ogg and archive.org are using. The
idea is that in future all media files will have the ability to do
temporal URIs (but also other types of fragment URIs like spatial or
tracks).

The W3C media fragments working group is right now in the process of
finalizing the first WD on this specification. You will be able to
comment on it soon - if you want to check out it's current incomplete
specification, it's here:
http://www.w3.org/2008/WebVideo/Fragments/WD-media-fragments-reqs/ .

Thus, the idea is that the <video> element should indeed support these
kinds of media fragments and that they are part of the URI rather than
an attribute.

The question whether it is more appropriate to display the URI time
offset in the video progress bar as the start time or whether it
should be 0 is indeed a tricky one. If we want to display that there
is some more context around the video, we should display the offset
time. I personally would prefer the latter option, since it relates
directly with the original resource.

I doubt though we need another attribute on the element - the
information is stored in the src URL, so should be retrieved from
there IMHO.

Cheers,
Silvia.


On Mon, Apr 6, 2009 at 8:52 AM, Chris Double <chris.double at double.co.nz> wrote:
> Ogg based media resources can start from a time position that is not
> zero. Examples of files that do this are those generated by the
> program oggz-chop. For example:
>
> http://ia331342.us.archive.org/2/items/night_of_the_living_dead/night_of_the_living_dead.ogv?t=0:20:00/0:20:50
>
> If this is played in VLC the start time of the video is 0:20:00. When
> seeking the time requested for the seek must be between 0:20:00 and
> 0:20:50. Does the HTML5 spec allow media resources that don't start
> from 0? I see in the spec mention:
>
> "Media elements have a current playback position, which must initially
> be zero. The current position is a time."
>
> In the case of the Ogg file above, the current playback position would
> initially be zero, but when the first frame is loaded it will be
> 0:20:00.
>
> Is this valid per the spec?  If so, would we need an attribute on the
> media object so the web page author can retrieve the start time of the
> video (in the same way they can get the duration). They would need
> this to be able to display progress bars/scrubbers to position the
> thumb correctly based on the currentTime. Detecting the first frame or
> metadata loaded events and getting the position of the that won't work
> as some of the video may have been played by the time that event is
> handled by user code.
>
> Chris.
> --
> http://www.bluishcoder.co.nz
>