pulseaudio recording: alsa capture volume levels are automatically reset

[cri]

Summary of the bug: when recording audio with -f pulse ffmpeg doesn't respect the alsa capture volume levels previously set with alsamixer or amixer.

How to reproduce:

amixer -c 0 set 'Capture' cap
amixer -c 0 set 'Capture' 20dB
amixer -c 0 set 'Internal Mic' cap
amixer -c 0 set 'Internal Mic Boost' 20dB

ffmpeg -f pulse -i alsa_input.pci-0000_00_1b.0.analog-stereo -ac 1 out.m4a

Expected result: ffmpeg should record audio using the volume levels I set with amixer.

Actual result: ffmpeg automatically resets audio levels: 'Capture' to 100%, 'Internal Mic Boost' to 0%

ffmpeg version 4.1.6 (Debian 10 package)

[Marton Balint]

I very much doubt that this has anything to do with ffmpeg. It's just the way pulse works ignoring the software volume controls of alsa?

I suggest you try capturing with parec/parecord and see if the issue happens there as well or not.

[cri]

Ah you're right, I finally found a clarification buried in the pulseaudio documentation:
​https://www.freedesktop.org/wiki/Software/PulseAudio/Documentation/User/PulseAudioStoleMyVolumes/

Basically, pulseaudio will automatically adjust the low-level alsa mixer controls (mic level and
boost) to match the capture level currently set in pulseaudio for the recording source.

In fact the example in my first post shows a wrong approach: i.e. set mixer controls using
ALSA tools and then record using ffmpeg -f pulse format.

The right way is to choose either ALSA or pulse, and use the proper tools for initial setup
and the proper ffmpeg -f option.

• ALSA: use amixer or alsamixer for setup, then use ffmpeg -f alsa...

• PA: use pactl or pavucontrol for setup, then use ffmpeg -f pulse...

I guess you can close this ticket.

[Marton Balint]

Ok, thanks, closed then.