[Live-devel] Add an audio sub-session makes the video stop

[Fabrice Triboix]

Dear Ross,

We implemented a class based on OnDemandServerMediaSubsession, and it 
uses an apparently widely used trick in live555 to get the "SDP lines". 
It plays the stream into a "dummy" RTP sink to get those lines and then 
stops the stream. That's where things were going wrong, because the RTP 
sink I was using for the MP3 audio sub-stream (MPEG1or2AudioRTPSink), if 
it is the one used for this trick) was not returning any SDP lines, and 
the system never gets out of this loop.

I fiddled a bit with that to try to get things working. I changed our 
subsession class so its "getAuxSDPLine()" method returns 
"rtpsink->auxSDPLine()", like it's done in the 
OnDemandServerMediaSubsession. It actually returns NULL, but it allowed 
me to move forward, as the DESCRIBE response is now coming with the SDP. 
I however noticed that the SDP part corresponding to the audio stream 
contains just one line "control=track2". This looks quite limited and 
one would expect to get at least the rtp profile...

So my question is: what exactly is 
"OnDemandServerMediaSubsession::getAuxDSPLine()"? When is it called? 
What should it return? I have not been able to find any documentation 
about that...

Anyway, VLC can now play the audio and the video, but for just half a 
second. Then the audio plays again after a glitch, but the video remains 
still. I can see in wireshark that both audio and video data are sent 
properly on their respective RTP ports... I probably need to investigate 
further, but I just wanted to know if you would have any clue about what 
could cause that.

Thank you so much for your help!

Best regards,

   Fabrice