[gst-devel] RTP Caps,base payloader and jrtplib

burgerman at users.sourceforge.net burgerman at users.sourceforge.net
Wed Nov 2 09:42:22 CET 2005

On Wed, 2 Nov 2005 18:09:20 +0200 (EET)
Kai Vehmanen <kvehmanen at eca.cx> wrote:

> Hi,
> On Wed, 2 Nov 2005, Thomas Vander Stichele wrote:
> >> Do you really need these values (ssrc, timestamp, sequence), in session
> >> descriptions? These are by nature random, and should be handled within the
> >> RTP stack.
> > Take for example an RTSP server.  The transport header in the RTSP reply
> > to a SETUP command should list the ssrc that is going to be used for
> > this RTP stream.  The RTP-Info header in the RTSP reply to a PLAY
> > command should list seq and rtptime at which the stream for that client
> > starts.  The RTP spec suggests that rtptime and seqnum start at a
> > randomized value.
> hmm, you're right. So the RTSP server needs a way to query the start 
> values for ts+seqno, and current ssrc. I'll leave it to burger to 
> comment how this fits with rtpbin... ;)

Currently the SSRC/ts start and seg start are generated randomly by the
payloader AND rtpbin. They are not generated by the RTSP element.
Therefore they are only generated after the stream is started or
elements created. So I don't see how this can help RTSP unless there is
a way to query these values from the payloader. So in any case why have
them inside the caps ? I am not saying these values will not be
available or will not be random, I am just saying they don't need to be
in the caps and they don't need and to be generated in the payloader,
since it is all already done in rtpbin. 
Does the stream go through the RTSP server BEFORE it sends the SETUP
reply and the PLAY commands so it can get the values from the CAPS ? 
I doubt it...
In the RTSP case, he would probably have to generate these values
before hand, but I don't see how the payloader can help and having them
in the caps can help it. I just wokeup, did I miss something there?

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