ALSA, MPD and Pulseaudio output capturing

2016-06-22

To be able to visualize my laptop’s sound output with a python script, I needed an extra audio input that made it possible to capture the system’s audio output.

To achieve that, I did the following on my Raspberry Pi:

install alsa-utils and pulseaudio
get the pulseaudio init script here
add the users to the group “pulse-access”, I got ALSA lib pulse.c:243:(pulse_connect) PulseAudio: Unable to connect without it even as root
create an ALSA monitor source

It is also possible to redirect audio to a FIFO.

MPD:

audio_output {
  type: "fifo"
  name: "FIFO"
  path: "/tmp/mpd.fifo"
  format: "44100:16:1"
}

Pulseaudio:

pacmd load-module module-pipe-sink file=/tmp/pulse.fifo
pacmd list-sinks  # search your default sink
pacmd load-module module-combine-sink slaves=yoursink,fifo_output
pacmd set-default-sink combined

ALSA:

pcm.writeFile {
  type file
  slave.pcm null
  file "/tmp/alsa.fifo"
  format "raw"
}