gUM audioCapture

by jib1

HTML

<audio id="audio" controls width="160" height="120" autoplay></audio><br>
Hit pause above to see that the audio comes from the element in this tab
<div id="container"></div>
<div id="div"></div>
<script src="https://webrtc.github.io/adapter/adapter-latest.js"></script>

JavaScript

const gUM = c => navigator.mediaDevices.getUserMedia(c);

// Requires media.getusermedia.audiocapture.enabled=true
(async () => {
  audio.srcObject = await gUM({audio: true, fake:true});
  spectrum(await gUM({audio: {mediaSource: "audioCapture"}}));
})().catch(e => log(e));

function spectrum(stream) {
  const audioCtx = new AudioContext();
  const analyser = audioCtx.createAnalyser();
  audioCtx.createMediaStreamSource(stream).connect(analyser);
  const [track] = stream.getAudioTracks();
  track.onended = () => audioCtx.close();
  track.stop_ = track.stop;
  track.stop = () => track.stop_(audioCtx.close());
  const canvas = container.appendChild(document.createElement("canvas"));
  canvas.width = audio.clientWidth;
  canvas.height = 200;
  const ctx = canvas.getContext("2d");
  const data = new Uint8Array(canvas.width);
  ctx.strokeStyle = 'rgb(0, 125, 0)';

  setInterval(() => {
    ctx.fillStyle = "#a0a0a0";
    ctx.fillRect(0, 0, canvas.width, canvas.height);
 
    analyser.getByteFrequencyData(data);
    ctx.lineWidth = 2;
    let x = 0;
    for (let d of data) {
      const y = canvas.height - (d / 128) * canvas.height / 4;
      const c = Math.floor((x*255)/canvas.width);
      ctx.fillStyle = `rgb(${c},0,${255-x})`;
      ctx.fillRect(x++, y, 2, canvas.height - y)
    }

    analyser.getByteTimeDomainData(data);
    ctx.lineWidth = 5;
    ctx.beginPath();
    x = 0;
    for (let d of data) {
      const y = canvas.height - (d / 128) * canvas.height / 2;
      x ? ctx.lineTo(x++, y) : ctx.moveTo(x++, y);
    }
    ctx.stroke();
  }, 1000 * canvas.width / audioCtx.sampleRate);
  return stream;
};

function log(msg) { div.innerHTML += "<br>" + msg; }