PulseAudio integration issues

[Conn]

On Wed, Aug 20, 2008 at 6:48 PM, Mackenzie Morgan <macoafi at gmail.com> wrote:
> Working PCM-multi-out (aka "software mixing"), because ALSA doesn't do
> mixing.  It gets rid of that thing where people complain because they
> can't get sound notifications from Pidgin while listening to music in
> Rhythmbox.  I think there are other things, but that's the only one I
> remember.

ALSA does support software mixing through the virtual device called
"dmix" (device mixer). Usually the default ALSA device is "dmix",
which is why ALSA applications can share sound on cards that do not
support hardware mixing (most cards nowadays, I think).

For all the complex features PulseAudio contains, it can be considered
a replacement for "dmix". PulseAudio is itself an ALSA client
(remember, it's a sound server, not a sound driver), but it needs
direct access to the hardware device in order to keep latency and CPU
usage low (unlike most ALSA applications). If the PulseAudio server is
active (i.e. playing sound), then the "dmix" device will become
unavailable. That is why, e.g. Totem and Rhythmbox can function
together (both use PulseAudio), but Totem and Flash cannot (Totem uses
PulseAudio, but Flash tries to use "dmix").

Setting the proper configuration in bug #198453 will instruct ALSA
applications (such as Flash) not to use "dmix", but pass their audio
to PulseAudio instead. As mentioned, some applications do not pass the
sound to PulseAudio correctly (e.g. Audacity), but they are most
certainly the minority.