Cannot capture sound directly from PCM channel

[Davide Cescato]

I would like to have a complete capture of my GNOME session, including
both the images displayed on my screen and the sound played by my
speakers. recordmydesktop does the job well as far as video capture is
concerned, but audio capture does not work as I wish. I would like
recordmydesktop to capture the sound from the PCM channel, but it
currently captures from the microphone(s) only.

I have a 64-bit F11/rawhide (updated as of today) system, with the
following packages:
* alsa-utils-1.0.20-3.fc11.x86_64
* recordmydesktop-0.3.8.1-1.fc11.x86_64
* gstreamer-0.10.22-3.fc11.x86_64
* gst-mixer-2.26.0-2.fc11.x86_64
* gnome-media-2.26.0-6.fc11.x86_64

My machine is a Lenovo Thinkpad W500. The output of alsa-info.sh is on
http://www.alsa-project.org/db/?f=e59e5f2c3b224d812abd1a44e6c1a2307091fe43

If I run alsamixer -c0, I see the following information:
Card: HDA Intel
Chip: Conexant CX20561 (Hermosa)

The following things are quite puzzling to me:
* the channels for the three microphones (internal, external, docking)
   appear under "Playback" but not under "Capture"
* none of the channels (including PCM) has a "capture" switch

If I run alsamixer without the -c0 option, I get only
Card: PulseAudio
Chip: PulseAudio
with a single "Master" playback channel and a single (switchable)
"Capture" channel.

I suspect the source of the problem lies within alsa, but it could
also be pulseaudio, or even gstreamer or recordmydesktop. I am not
sure if this is a bug, and this is why I am posting here.

Does anyone understand what is wrong in my setup and how I can get PCM
capture working?