Re: Do we need to support media that doesn't start at 0?

Jack,

On 13/04/2011 13:58, Jack Jansen wrote:
>
> On Apr 13, 2011, at 12:03 , Philip Jägenstedt wrote:
>
>>  From todays teleconf.
>>
>> The question comes up in some test cases in<http://www.w3.org/2008/WebVideo/Fragments/TC/ua-test-cases.html>.
>>
>> It it my experience that media not starting at time 0 is extremely rare, I've really only seen it in poorly remuxed MPEG-2 transport streams and similar. I would say that *if* a user agent supports media that doesn't start at 0, then we should clamp the request start to the start time when necessary. I don't think that we should make the start/end relative to the media start position, as that would be inconsistent.
>
>
> Everyone seems to say "we don't want to support media that doesn't start at t=0", but then my next question is:
>
> Assuming I have an item example.ogv starting at t=0. I now request<http://example.com/example.ogv?t=10,20>. Does the resulting video stream start at t=0 (i.e. has everything been recoded, if the underlying format has embedded timestamps) or at t=10, or do we simply leave it implementation-defined?
Our implementation within NinSuna will create a new resource, starting 
at timestamp 0 (since it's a query parameter). For example, 
http://ninsuna.elis.ugent.be/Media/MFWG/TC/spatial_30fps.webm?t=5,10 
creates a new media resource starting at 0s and ending at 5s.

> And, of course, the next question is: what does<http://example.com.ogv?t=10,20#t=5,15>  show? seconds 5-10 of the original media file? seconds 10-15 of the original media file? Something else?
This comes down to the following HTTP request (using time range requests):
GET http://example.com.ogv?t=10,20
Range: t:npt=5,15

Requesting http://example.com.ogv?t=10,20 results in a new media 
resource starting at 0s and having a duration of 10s. Applying a time 
fragment request from 5s to 15s will result in a response of the last 5s 
of http://example.com.ogv?t=10,20. Or in other words, seconds 15 to 20 
of http://example.com.ogv (not taking into account random access points 
here).

This is the way it works today in NinSuna.

Best regards,

Davy

-- 
Davy Van Deursen

Ghent University - IBBT
Department of Electronics and Information Systems - Multimedia Lab
URL: http://multimedialab.elis.ugent.be/dvdeurse

Received on Wednesday, 13 April 2011 12:16:37 UTC