[vlc-devel] multicast multi-contributor RTP

Rémi Denis-Courmont remi at remlab.net
Mon Aug 15 18:22:52 CEST 2011

Le lundi 15 août 2011 18:38:33 Barker, Mark, vous avez écrit :
> 1) is is possible to setup an RTP multicast stream with multiple speakers?

In theory, the rtp-max-src parameter can be increased to support multiple 
speakers. They will then show up as as many audio tracks. This is however 
untested, and some hidden bugs are not unlikely to show.

Furthermore, the default VLC stream policy selects only one audio track at a 
time. Playing multiple audio tracks is feasible but not straightforward:

# vlc --rtp-max-src 10 --sout-all --sout '#display'

> - I can't work this out from the documentation and trial and error has
> failed me from the cvlc command line - any ideas? I'd also be interested
> in knowing anything about the possibility to use VLC in demuxing and
> handling individual speaker streams in independent pipelines.

That is possible with source-specific multicast, or a single group per speaker 
or at least a different destination port per speaker. However, cvlc is mostly 
designed to deal with a single pipeline, or unsupervised with VLM. In other 
words, you would probably need to write a custom interface or tap directly 
into the LibVLC programming interface.

Otherwise, each speaker is an independent audio track in the same pipeline, 
which severely limits the ability to control them individually.

> 2) when using a microphone source via alsa for speaking onto such a stream,
> is it possible to control the RTP and audio characteristics of the stream
> data - e.g. things like SSRC (and making it individual for each speaker),

You cannoy select the SSRC as it is. It would probably not be very hard to 
support, but I do not see the point.

> sampling frequency,

You can either request a specific sample rate from ALSA, or you can force 

> packet duration, etc...

Not sure.

> again, if this is possible
> from cvlc, can anybody provide me with a command-line to do so?

Rémi Denis-Courmont

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