Finally possible to capture monitor devices in Chromium and Chrome on Linux

gdm_capture_monitor_device_on_chromium.js

// Finally possible to capture speechSynthesis.speak() on Chromium and Chrome
// Enable Speech Dispatcher, PulseAudio loopback for screen capture, disable default WebRTC input volume adjustment from 100% to 8% 
// chrome --enable-speech-dispatcher --enable-features=PulseaudioLoopbackForScreenShare --disable-features=WebRtcAllowInputVolumeAdjustment
// Still have to manually select share system audio in picker with systemAudio set to "include"
// https://issues.chromium.org/issues/40155218
let stream = await navigator.mediaDevices.getDisplayMedia({
  // We're not going to be using the video track
  video: {
    width: 0,
    height: 0,
    frameRate: 0,
    displaySurface: "monitor"
  },
  audio: {
    suppressLocalAudioPlayback: false,
    // Speech synthesis audio output is generally 1 channel
    channelCount: 2,
    noiseSuppression: false,
    autoGainControl: false,
    echoCancellation: false
  },
  systemAudio: "include",
  // Doesn't work for Tab capture
  // preferCurrentTab: true
});

function log(e, ...args) {
  if (e?.target) {
    console.log(e.target.constructor.name, e.type);
  } else {
    console.log(...args);
  }
};

let [videoTrack] = stream.getVideoTracks();

videoTrack.stop();

let [audioTrack] = stream.getAudioTracks();

log(null, audioTrack.constructor.name, audioTrack.kind, audioTrack.getSettings().deviceId);

let recorder = new MediaRecorder(stream);

recorder.onstart = log;

recorder.onstop = (e) => {
  recorder.stream.getTracks().forEach((track) => track.stop()); 
  log(e);
};

recorder.ondataavailable = (e) => {
  console.log(URL.createObjectURL(e.data));
  log(e);
};

let utterance = new SpeechSynthesisUtterance(`von Braun believed in testing. I cannot
emphasize that term enough – test, test,
test. Test to the point it breaks.

- Ed Buckbee, NASA Public Affairs Officer, Chasing the Moon`);

utterance.onstart = (e) => { 
  recorder.start(); 
  log(e);
};

utterance.onend = (e) => {
  recorder.stop(); 
  log(e);
};

globalThis.speechSynthesis.speak(utterance);