Is it possible to get raw values of audio data using MediaRecorder()

user_10362955 0
Viewed 1672

I'm using MediaRecorder() with getUserMedia() to record audio data from the browser. It works, but recorded data is recorded in the Blob format. I want to get raw audio data (amplitudes), not the Blobs. Is it possible to do it?

My code looks like this:

  navigator.mediaDevices.getUserMedia({audio: true, video: false}).then(stream => {
    const recorder = new MediaRecorder(stream);
    recorder.ondataavailable = e => {
      console.log(e.data); // output: Blob { size: 8452, type: "audio/ogg; codecs=opus" }
    };
    recorder.start(1000); // send data every 1s
  }).catch(console.error);
web-mediarecorder webrtc mediarecorder javascript
3 Answers

MediaRecorder is useful to create files; if you want to do audio processing, Web Audio would be a better approach. See this HTML5Rocks tutorial which shows how to integrate getUserMedia with Web Audio using createMediaStreamSource from Web Audio.

user_1395910

No need for MediaRecorder. Use web audio to gain access to raw data values, e.g. like this:

navigator.mediaDevices.getUserMedia({audio: true})
.then(spectrum).catch(console.log);

function spectrum(stream) {
  const audioCtx = new AudioContext();
  const analyser = audioCtx.createAnalyser();
  audioCtx.createMediaStreamSource(stream).connect(analyser);

  const canvas = div.appendChild(document.createElement("canvas"));
  canvas.width = window.innerWidth - 20;
  canvas.height = window.innerHeight - 20;
  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);
};
user_9189100

I used the following code to achieve an array of integers into console. As to what they mean, I assume they are amplitudes.

const mediaRecorder = new MediaRecorder(mediaStream);
mediaRecorder.ondataavailable = async (blob: BlobEvent) => console.log(await blob.data.arrayBuffer());
mediaRecorder.start(100);

If you were to want to draw them, then I found this example that I had forked on codepen: https://codepen.io/rhwilburn/pen/vYXggbN which pulses the circle once you click on it.

user_10745140
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