Record a programs output with PulseAudio

Question

I would like to record an output of a program with PulseAudio using command line/bash script. It is important not to record every output of the sound card, but only the one of one specific program. I thought I would have to create a new null-sink and than move the programs output to this new sink. Than tell parec to use this specific monitor to record. The first step would be something like this:

pactl load-module module-null-sink sink_name=steam

But how to move the programs output now to this sink? And how to record the specific sink with a bash script?

Answer 1

Try something like this:

In a terminal enter

pacmd

(this is the CLI of the PulseAudio-Server) then use

list-sink-inputs

(where you get the indices of the running inputs) Now find the index of your input. Now referred to as $INDEX

the scriptable part is:

pactl load-module module-null-sink sink_name=steam
pactl move-sink-input $INDEX steam
parec -d steam.monitor | oggenc -b 192 -o steam.ogg --raw -

Explanations:

• The first command will add a null-sink as you already knew.
• The second command moves the sink-input from your standard-audio-sink to steam
• The third command records the monitor of the device steam (-d) and puts the output (raw-wave-stream) into oggenc, which encodes this wave-stream to an oga-file. (for mp3 use lame)

Greez Waschtl

Answer 2

@Waschtl's answer is fantastic. @ixtmixilix asked about restoring regular audio after the recording is finished. Here's the easiest way I know of:

Install and run the pavucontrol GUI. You should see your audio-outputting application and it's volume meter under the Playback tab in there. There will be a button next to it showing that it's playing on Null Output. Click on that and change it to your ordinary audio output, Built-in Audio Analog Stereo in my case.

Here's a screenshot of what you're looking for:

You can also use this approach to set up your recording in the future, after you've run the load-module command in @Waschtl's answer to create the sink.