[pulseaudio-discuss] Sync'd output on several computers in heterogeneous network

Lennart Poettering lennart at poettering.net
Mon May 28 15:53:05 PDT 2007

On Sun, 13.05.07 13:28, Svein Halvor Halvorsen (pulse at svein.halvorsen.cc) wrote:


> Hi, again!
> I also have a question regarding a home entertainment setup:
> I live in a shared apartment with some other people. We're all students, 
> and we've got an mpd server hooked up to an amplifier in our living 
> room. In addition, we all got computers hooked up to our own stereo 
> systems in all our rooms, and it would be nice to have the same music 
> playing everywhere in our apartment, eg. when we're having parties.
> So: If I use the rtp multicast thing, will all the clients (one Ubuntu, 
> one FreeBSD, one Mac OS X and two Windows 'puters) be synchronized? Cuz, 
> when you're standing in the hallway, you'll be hearing several of the 
> loudspeakers at the same time, and we don't want echo. (A little reverb 
> might be ok, as long as it's not annoying to listen to).
> Would this be better served by running a pulseaudio server on each of 
> the computers, and have the "source" pulseaudio server 
> forward/tunnel/whatever to the "sink" servers?
> We don't care if there's some latency, as long as all clients are in 
> sync, as this is only for music, and not video.

Actually Multicast RTP would be the most elegant solution for
this. However, right now we do not implement adaptive sample rate
adjustments for RTP receivers. That means that audio will start to
deviate more and more over time. When standing at the door between two
rooms this will result in a strange stereo effect that grows larger
and larger and eventually becomes an echo. If the deviation gets too
large one machine might skip a few simples or pause for a few
samples. While this might be OK for occasional listening to music, it
will probably annoy the hell out of you if you live with this for a
longer time. (Ohm and it's definitely nothing that would impress anyone
at a party - right the contrary ;-))

Someone on this ML or on IRC once reported that running module-combine
on top of a few module-tunnel instances works. Actually I am quite
surprised that it does, but you might want to try that. Of course
using this solution increases the imposed network traffic quite a bit
and is also far less automatic (in the sense of plugnplay)

Adding proper sample freq deviation handling to the RTP modules is on
my todo list --- among a lot of other stuff.

Also, PA has not been ported to MacOSX yet. Porters welcome!

Have fun!


Lennart Poettering                        Red Hat, Inc.
lennart [at] poettering [dot] net         ICQ# 11060553
http://0pointer.net/lennart/           GnuPG 0x1A015CC4

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