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RE: a quick scan of RTSP for media fragments

From: Davy Van Deursen <davy.vandeursen@ugent.be>
Date: Wed, 30 Jun 2010 15:08:27 +0200
To: "'Silvia Pfeiffer'" <silviapfeiffer1@gmail.com>, 'RaphaŽl Troncy' <raphael.troncy@eurecom.fr>
Cc: "'Jack Jansen'" <Jack.Jansen@cwi.nl>, <public-media-fragment@w3.org>
Message-ID: <000801cb1855$547176c0$fd546440$@ugent.be>
Hi Jack, Silvia,

> -----Original Message-----
> From: public-media-fragment-request@w3.org [mailto:public-media-fragment-request@w3.org] On Behalf Of Silvia Pfeiffer
> Sent: woensdag 30 juni 2010 11:54
> To: RaphaŽl Troncy
> Cc: Jack Jansen; Davy Van Deursen; public-media-fragment@w3.org
> Subject: Re: a quick scan of RTSP for media fragments
> 
> 2010/6/30 RaphaŽl Troncy <raphael.troncy@eurecom.fr>:
> > Hi all,
> >
> >> I agree with all of your examples (thanks!), except one:
> >>
> >>> Re (1): In RTSP, temporal fragment URIs are provided through the
> >>> PLAY method:
> >>>
> >>> a url such as
> >>>
> >>> rtsp://example.com/media#t=10,20
> >>>
> >>> will be executed as a series of the following methods (all shortened
> >>> for readability), data selection provided in the PLAY
> >>> method:
> >>>
> >>> * C->S: DESCRIBE rtsp://example.com/media * S->C: RTSP/1.0 200 OK
> >>> (with an SDP description, see wiki) * C->S: SETUP
> >>> rtsp://example.com/media/video * S->C: RTSP/1.0 200 OK * C->S:
> >>> SETUP rtsp://example.com/media/audio * S->C: RTSP/1.0 200 OK *
> >>> C->S: PLAY rtsp://example.com/media Range: npt=10-20 * S->C:
> >>> RTSP/1.0 200 OK Range: npt=9.5-20.1
> >>
> >>
> >> Why do you use two SETUP commands for separate tracks here? Shouldn't
> >> you simply do a single "SETUP rtsp://example.com/media"?
> >
> > Good question! Silvia?
> 
> See section "14.2 Streaming of a Container file" - the example also uses all tracks for setup and not the combined format, even
though
> it is dealing with a container format. I just followed that example. I couldn't find out from the spec whether a single SETUP is
actually
> possible (it seemed to me that not), but if it is, I'm more than happy to change that.

Indeed, within RTSP, each streamed track corresponds to an RTSP subsession, and each subsession needs to be setup separately. In the
spec, you can find in section 10.4: "The SETUP request for a URI specifies the transport mechanism to be used for the streamed
media. A client can issue a SETUP request for a  stream that is already playing to change transport parameters, which  a server MAY
allow.". In section 1.3, you can find the definition of a stream: "A single media instance, e.g., an audio stream or a video  stream
as well as a single whiteboard or shared application  group. ...". I agree that it is not perfectly clear from the spec :-), but I
am pretty confident (based on my implementation experience) that a SETUP command is coupled to media streams (or tracks) and not to
the whole RTSP session.

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, 30 June 2010 13:08:54 GMT

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