[pulseaudio-discuss] Virtual loopback to provide PCM capture

[Davide Cescato]

Hello,

thanks for the work on PulseAudio! I would like to ask a question, and 
will try to be as precise as I my limited knowledge allows.

I would like to capture the audio on the PCM channel, i.e., the mixed 
sound stream that is sent to my notebook's speakers. I have read in 
forums that Windows Vista achieves the behaviour I am aiming at by 
offering a virtual audio channel called "what you hear" among the list 
of capture sources. I do not have Windows Vista, so I could not see this 
working myself.

I would however like to do the same in Fedora 11. So I wonder if 
Pulseaudio can create a "virtual loopback" by taking the PCM channel and 
feeding it back (besides sending it to the speakers, of course) into a 
sound capture channel that can then be selected as the default capture 
source that sound-capturing applications will use (actually, I would 
like to use recordmydesktop to simultaneously capture video and audio of 
my desktop session).

I am not sure if providing this capability is a job for PA. In fact, I 
actually had first filed a bug against ALSA on the topic 
(https://bugzilla.redhat.com/show_bug.cgi?id=502293) but I had little 
luck. Then I thought that since the issue is about routing audio 
streams, it may definitely fall into the scope of PA. Being far from an 
expert on the matter, I apologize for the noise if this is not the case. 
I would however be curious to know if PA currently provides any solution 
to this issue, and if not, whether this could happen soon in a future 
version.

Thanks!