[Live-devel] track synchronization with live555

[David Betrand]

Ross,

> It does, however, make this header information available for clients
> to use - see "MediaSession.hh".

I know but the only place where this struct is filled in is within RTSPClient class. And having a look at parseRTPInfoHeader(), I see that only the first track is parsed in this header so I guess this is a bug in the library.
> 
> You're correct, though, that the RTP-Info header information is the
> only way to generate a proper presentation time for RTP packets that
> arrive before the first RTCP SR packet.
I think it is even more "incorrect" than that in the library now. Even after receiving the first SR, your presentation times are not coherent in some circumstances. This is because you compute fSyncTime first with timeNow, and then with the SR NTP, confusing NPT and NTP. You should use those SR another way, by comparing your wall clock with the wall clock  of the sender. My example in my previous mail clearly illustrates this case.
  The VLC developers (in
> particular, Derk-Jan Hartman) tell me that they are currently
> modifying VLC to use the RTP-Info header information upon
> initialization.

I saw this thread and had a look at the VLC code. Apparently, VLC only needs the sequence numbers present in this rtp-info header. This is useful for seeking and pausing/resuming the stream

  At some point I should probably modify the LIVE555
> "RTSPClient" code to do this automatically, so that each client
> application developer doesn't have to deal with this himself.
As the way I see it is quite different from the current implementation, what I could suggest is to send a patch with a IFDEF clause, allowing to switch between a SR-based synchronization (current implementation), and a  rtp-info-based synchronization ? Would it be a good start for you ?
> 
> Note, though, that not all RTP receivers use RTSP (or SIP) for
> set-up, and so not all will have "RTP-Info" information available.
> These receivers must be prepared to deal with inaccurate presentation
> times prior to the arrival of the first RTCP SR.
Yes I know, and my application DOES care about such clients (in particular SIP clients) so we will try to handle those also in the patch

Best Regards,
David
> --
> 
> Ross Finlayson
> Live Networks, Inc.
> http://www.live555.com/
> _______________________________________________
> live-devel mailing list
> live-devel at lists.live555.com
> http://lists.live555.com/mailman/listinfo/live-devel

>


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