Chromium does not support capture of monitor devices by default

[guest271314]

Chromium does not support capture of monitor devices by default https://bugs.chromium.org/p/chromium/issues/detail?id=1114422.

Workarounds https://github.com/guest271314/captureSystemAudio.

[guest271314]

Workaround for https://bugs.chromium.org/p/chromium/issues/detail?id=931749#c6 where Chromium refuses to support listing or capturing monitor devices https://bugs.chromium.org/p/chromium/issues/detail?id=1155954#c_ts1607798815.

$ pactl load-module module-remap-source \
  master="$(pactl list | grep -A2 'Source #' | grep 'Name: .*\.monitor$' | cut -d" " -f2)" \
  source_name=virtmic source_properties=device.description=Virtual_Microphone

$ pactl set-default-source virtmic

See https://github.com/guest271314/captureSystemAudio#pulseaudio-module-remap-source.

[guest271314]

To capture speech-dispatcher-espeak-ng module at Linux on Chromium or Chrome we create a virtual device and remap the monitor thereof to a different name to avoid Chrome refusing to list or capture monitor devices

pactl load-module module-combine-sink \
sink_name=Web_Speech_Sink slaves=$(pacmd list-sinks | grep -A1 "* index" | grep -oP "<\K[^ >]+") \
sink_properties=device.description="Web_Speech_Stream" \
format=s16le \
channels=1 \
rate=22050

pactl load-module module-remap-source \
master=Web_Speech_Sink.monitor \
source_name=Web_Speech_Monitor \
source_properties=device.description=Web_Speech_Output

pactl move-sink-input $(pacmd list-sink-inputs | tac | perl -E'undef$/;$_=<>;/speech-dispatcher-espeak-ng.*?index: (\d+)\n/s;say $1') Web_Speech_Sink

We can then select device with label 'Web_Speech_Output'

navigator.mediaDevices.getUserMedia({audio: true})
.then(async stream => {
  const [track] = stream.getAudioTracks();
  const devices = await navigator.mediaDevices.enumerateDevices();
  const device = devices.find(({label}) => label === 'Web_Speech_Output');
  if (track.getSettings().deviceId === device.deviceId) {
    return stream;
  } else {
    track.stop();
    console.log(devices, device);
    return navigator.mediaDevices.getUserMedia({audio: {deviceId: {exact: device.deviceId}}});
  }
})
.then(stream => {
  const recorder = new MediaRecorder(stream);
  recorder.ondataavailable = e => console.log(URL.createObjectURL(e.data));
  const synth = speechSynthesis;
  const u = new SpeechSynthesisUtterance('test');
  u.onstart = e => {
    recorder.start();
    console.log(e);
  }
  u.onend = e => {
    recorder.stop();
    recorder.stream.getTracks().forEach(track => track.stop());
    console.log(e);
  }
  synth.speak(u);
});

References:

• https://askubuntu.com/questions/60837
• https://aweirdimagination.net/2020/07/19/virtual-microphone-using-gstreamer-and-pulseaudio/

[guest271314]

Workaround for https://bugs.chromium.org/p/chromium/issues/detail?id=931749#c6 where Chromium refuses to support listing or capturing monitor devices https://bugs.chromium.org/p/chromium/issues/detail?id=1155954#c_ts1607798815.

$ pactl load-module module-remap-source \
  master="$(pactl list | grep -A2 'Source #' | grep 'Name: .*\.monitor$' | cut -d" " -f2)" \
  source_name=virtmic source_properties=device.description=Virtual_Microphone

$ pactl set-default-source virtmic

See https://github.com/guest271314/captureSystemAudio#pulseaudio-module-remap-source.

This evidently no longer works on Chromium 104. Records only silence.

[guest271314]

Workarounds working again on Chrome 106.