[pulseaudio-discuss] Controlling where module-rtp-send sends multicast packets?

Matt Patterson matt at v8zman.com
Fri Feb 15 14:51:46 PST 2008

I tried setting the routing table to direct to other interfaces but the 
packets keep appearing on the interface i didn't want. Each of the 4 rtp 
send modules goes to a different multicast address, so I figured that 
would be easy to route. It is fully possible that I was specifying the 
route incorrectly, so I will double check that.

The reason for multicasting was allowing the sinks to connect to any of 
the four players while they were in operation, no interuption. That way 
any or all zones can connect to any mpd stream at will without interuption.

It is very good to know though that the rtp module has no sync feedback 
(at least not to the crystal level). I have tested playing back 4 rtp 
receiver modules at once on the same machine and notice echoing effects, 
so I knew the sync wasn't perfect, but close, and probably good enough 
for room to room.

I think I am going to investigate the combine module route more as per 
Tanu's suggestion. That should give me the better sink solution with 
hopefully tolerable processor/memory loads. I am on a core 2 duo 
machine, and all the outputs will be on one 8 channel sound card, so in 
theory syncing won't hurt too much.

Thanks for the info Lennart.


Lennart Poettering wrote:
> On Thu, 14.02.08 22:23, Matthew Patterson (matt at v8zman.com) wrote:
>> Now for my question: This implementation obviously spews a lot of 
>> multicast traffic onto my network. I didn't think this would be a 
>> problem, but my router/ap/switch seems to crap out when it gets hammered 
>> with all the traffic. Is there any way that I can specify which 
>> interface pulesaudio sends its multicast packets on? 
> Yes, it's called the "Routing Table" of your IP stack. Just use a
> seperate mcast group for each destination. And then add routes for the
> specific group to the right interface. 
> Plese note that the RTP module doesn't deal with deviating
> crystals. Might not be that great on the long run for the real Hifi
> experience.
>> Or even more ideally, can I disable all outgoing multicast traffic
>> and just have the local loopback happening?
> Hmm? This makes no sense. Why would you use mcast then at all?
> Lennart
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