Hi Ross,
Connecting a RTSP client to receive a multicast RTP stream should not
change the RTP stream at all - so (unless you have a firewall
or other middlebox somewhere that is altering the RTP stream) there
must be a mistake in the way that your RTSP server application
is delivering this stream.
I believe, there still needs to be a RTSP handshake for VLC to join the
multicast stream.
This is code which has run for many years. The change I made recently
was to calculate the presentation time for each frame based on
the frame-rate, eg 40ms for 25fps, rather than calling gettimeofday()
for every frame. Without this change, VLC was displaying a jerky video
stream. The change in presentationtime calculation fixed this jitter but
has led to this new issue, where multiple VLC sessions can cause
a huge jump in presentation time.
I can't debug this without seeing your server code (in particular, how
you're using "RTSPServer").
However, to start, you should run the existing "testH264VideoStreamer"
demo application (in the "testProgs" directory),
and make sure that this works correctly for you on your network (with
multiple RTSP clients).
Then, compare the code for that application with your code, to see what
is going wrong. (Note, in particular, that -
to deliver a multicast stream - your server needs to use a
"PassiveServerMediaSubsession" rather than an
"OnDemandServerMediaSubsession"
(which is meant only for delivering a stream via unicast).)
Yes I use PassiveServerMediaSubsession for the multicast stream. I'm
sure it's a corruption of presentation time which is causing the issue,
but this does not seem to be in my code. I have added debug to every
place where fPresentationTime is changed.
I have tried to attach a screenshot of the wirshark trace so you can see
how the time jumps for one consecutive frame to the next when a
VLC session is started and connected.
- David
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