How can I extract the preceding audio (from microphone) as a buffer when silence is detected (JS)?

Question

I\'m using the Google Cloud API for Speech-to-text, with a NodeJS back-end. The app needs to be able to listen for voice commands, and transmit them to the back-end as a buf

Answer 1

I'm not too sure as to what exactly is being asked in the question, so this answer is only intended to give a way to detect silences in an AudioStream.

---

To detect silence in an AudioStream, you can use an AudioAnalyser node, on which you will call the getByteFrequencyData method at regular intervals, and check whether there were sounds higher than than your expected level for a given time.

You can set the threshold level directly with the minDecibels property of the AnalyserNode.

function detectSilence(
  stream,
  onSoundEnd = _=>{},
  onSoundStart = _=>{},
  silence_delay = 500,
  min_decibels = -80
  ) {
  const ctx = new AudioContext();
  const analyser = ctx.createAnalyser();
  const streamNode = ctx.createMediaStreamSource(stream);
  streamNode.connect(analyser);
  analyser.minDecibels = min_decibels;

  const data = new Uint8Array(analyser.frequencyBinCount); // will hold our data
  let silence_start = performance.now();
  let triggered = false; // trigger only once per silence event

  function loop(time) {
    requestAnimationFrame(loop); // we'll loop every 60th of a second to check
    analyser.getByteFrequencyData(data); // get current data
    if (data.some(v => v)) { // if there is data above the given db limit
      if(triggered){
        triggered = false;
        onSoundStart();
        }
      silence_start = time; // set it to now
    }
    if (!triggered && time - silence_start > silence_delay) {
      onSoundEnd();
      triggered = true;
    }
  }
  loop();
}

function onSilence() {
  console.log('silence');
}
function onSpeak() {
  console.log('speaking');
}

navigator.mediaDevices.getUserMedia({
    audio: true
  })
  .then(stream => {
    detectSilence(stream, onSilence, onSpeak);
    // do something else with the stream
  })
  .catch(console.error);

And as a fiddle since stackSnippets may block gUM.