Red Hat Bugzilla – Bug 502293
Cannot capture audio directly from PCM channel
Last modified: 2009-10-29 12:33:16 EDT
Description of problem:
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.
Version-Release number of selected component (if applicable):
F11 rawhide updated as of 2009-05-22. Here are the versions of a few packages I estimate as relevant:
Steps to Reproduce:
1. run rgtk-recordMyDesktop
2. start recording with sound
3. try again after changing settings in alsamixer -c0
Sound capture always goes through the active microphone (be it the notebook's internal microphone or a plugged-in external microphone). There is no way to capture the PCM channel directly. alsamixer -c0 does not offer a "CAPTUR" switch on the PCM channel.
Possibility to capture audio from directly the PCM channel and not from the active microphone.
The notebook is a Lenovo Thinkpad W500.
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
with a single "Master" playback channel and a single (switchable)
I suspect the source of the problem lies within alsa, but it could
also be pulseaudio, or even gstreamer?
I also wonder if bug 487794 is related, since it is about a Conexant cx20561 (Hermosa) codec. I am not affected by that bug, though.
Since there was no reaction so far, I wonder if I have filed the bug under the correct component. Should it be reassigned to alsa-lib, gnome-media, gstreamer, pulseaudio?
The hardware does not support requested feature (unless you turn on analog loopback which is also not supported on all codecs - see 'amixer controls').
You can obtain playback PCM stream using tee plugin (alsa-lib) or use snd-aloop kernel driver.
Regarding PA - I don't know if it's possible to capture playback stream in PA.
This bug appears to have been reported against 'rawhide' during the Fedora 11 development cycle.
Changing version to '11'.
More information and reason for this action is here:
Thanks for your reply. It looks like there is no 'Analog Loopback' mixer control with my codec, as 'amixer controls' returns
numid=4,iface=MIXER,name='Master Playback Switch'
numid=3,iface=MIXER,name='Master Playback Volume'
So I have to try the other two options. Could you point me to some documentation about the ALSA tee plugin?
And... Could you please confirm that snd-aloop is not packaged for Fedora? If this is the case, I will mark this bug as a duplicate of bug 496200.
alsa-lib example (the string after -D is device name for alsa-lib):
aplay -D tee:SLAVE=\"plughw:0\",FILE=/tmp/abcd.raw <some_wav_file>
And yes, snd-aloop is not in mainstream or Fedora kernels.
*** This bug has been marked as a duplicate of bug 496200 ***
I think that snd-aloop is not in the kernel because of pulse-audio..
I installed pavucontrol. pulseaudio volume control
launch pavcontrol, select input devices.
select the drop down menu at the bottom right and select 'all input devices'
then you will see 'monitor of <your sound card>' my was SB Audigy so I selected that.
then I used pulse to record in recordmydesktop and It worked I had sound. that is if you want to record sound from your desktop and not from your microphone, if you want your microphone select the device that is your microphone.