[pulseaudio-discuss] using pulseaudio with simultaneous playback from mutiple X sessions

Colin Guthrie gmane at colin.guthr.ie
Wed Nov 9 03:32:49 PST 2011

'Twas brillig, and Martin Steigerwald at 09/11/11 10:43 did gyre and gimble:
> I would even do not have any problem when there would still be two session 
> based pulseaudio daemons just using dmixing for audio output and grabbing 
> input for recording explicitely. Only then there would need to be some 
> mechanism to decide which user gets recording. It could by on a case base, 
> so that Pulseaudio grabs input sinks only on demand. And it should not be 
> possible to record the dmixed audio output by any user. Each user may only 
> record his own audio output.
> Maybe thats a workable idea?

It's possible. Just configure the default.pa to use dmix for it's alsa
sink, and then ensure that you set the profile for the udev-detected
card for each user to an input only profile such that it doesn't create
a sink too.

Of course dmix adds overhead, messes about with timing, and screws up
sample rate conversion (and uses the shitty quality resamplers too), but
other than that it would work OK.

Unless the card supports hardware mixing, the recording would only work
for the first user to get it as the other tasks would fail. This is of
course a hideous setup with horrible connotations for handling
gracefully in UIs etc the cases when the audio doesn't work... It's
certainly not something I'd be able to recommend with a straight face.



Colin Guthrie

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