audioAnalyser.js

const audioCtx = new(window.AudioContext || window.webkitAudioContext)();
const analyser = audioCtx.createAnalyser();


analyser.fftSize = 2048;
let bufferLength = analyser.frequencyBinCount;
let dataArray = new Uint8Array(bufferLength);
analyser.getByteTimeDomainData(dataArray);

let canvas = document.getElementById("oscilloscope");
let canvasCtx = canvas.getContext("2d");


function draw() {

  drawVisual = requestAnimationFrame(draw);

  analyser.getByteTimeDomainData(dataArray);

  canvasCtx.fillStyle = 'rgb(200, 200, 200)';
  canvasCtx.fillRect(0, 0, canvas.width, canvas.height);

  canvasCtx.lineWidth = 2;
  canvasCtx.strokeStyle = 'rgb(0, 0, 0)';

  canvasCtx.beginPath();

  let sliceWidth = canvas.width * 1.0 / bufferLength;
  let x = 0;

  for (let i = 0; i < bufferLength; i++) {

    let v = dataArray[i] / 128.0;
    let y = v * canvas.height / 2;

    if (i === 0) {
      canvasCtx.moveTo(x, y);
    } else {
      canvasCtx.lineTo(x, y);
    }

    x += sliceWidth;
  }

  canvasCtx.lineTo(canvas.width, canvas.height / 2);
  canvasCtx.stroke();
};

draw();