var
btn = document.querySelector("button"),
canvas,
cStream,
aStream,
vid,
recorder,
analyser,
dataArray,
bufferLength,
chunks = [];
function clickHandler() {
btn.textContent = 'stop recording';
if (!aStream) {
initAudioStream();
}
cStream = canvas.captureStream(30);
cStream.addTrack(aStream.getAudioTracks()[0]);
recorder = new MediaRecorder(cStream);
recorder.start();
recorder.ondataavailable = saveChunks;
recorder.onstop = exportStream;
btn.onclick = stopRecording;
};
function exportStream(e) {
if (chunks.length) {
var blob = new Blob(chunks, { type: chunks[0].type });
var vidURL = URL.createObjectURL(blob);
var vid = document.createElement('video');
vid.controls = true;
vid.src = vidURL;
vid.onend = function() {
URL.revokeObjectURL(vidURL);
}
document.body.insertBefore(vid, canvas);
} else {
document.body.insertBefore(document.createTextNode('no data saved'), canvas);
}
}
function saveChunks(e) {
e.data.size && chunks.push(e.data);
}
function stopRecording() {
vid.pause();
btn.remove();
recorder.stop();
}
function initAudioStream() {
var audioCtx = new AudioContext();
var dest = audioCtx.createMediaStreamDestination();
aStream = dest.stream;
var sourceNode = audioCtx.createMediaElementSource(vid);
sourceNode.connect(dest)
vid.play();
analyser = audioCtx.createAnalyser();
sourceNode.connect(analyser);
analyser.fftSize = 2048;
bufferLength = analyser.frequencyBinCount;
dataArray = new Uint8Array(bufferLength);
analyser.getByteTimeDomainData(dataArray);
sourceNode.connect(audioCtx.destination)
startCanvasAnim();
}
function enableButton() {
vid.oncanplay = null;
btn.onclick = clickHandler;
btn.disabled = false;
};
var loadVideo = function() {
vid = document.createElement('video');
vid.crossOrigin = 'anonymous';
vid.oncanplay = enableButton;
vid.src = 'https://dl.dropboxusercontent.com/s/bch2j17v6ny4ako/movie720p.mp4';
}
function startCanvasAnim() {
canvas = Object.assign(document.createElement("canvas"), { width: 500, height: 200});
document.body.prepend(canvas);
var canvasCtx = canvas.getContext('2d');
canvasCtx.fillStyle = 'rgb(200, 200, 200)';
canvasCtx.lineWidth = 2;
canvasCtx.strokeStyle = 'rgb(0, 0, 0)';
var draw = function() {
var drawVisual = requestAnimationFrame(draw);
analyser.getByteTimeDomainData(dataArray);
canvasCtx.fillRect(0, 0, canvas.width, canvas.height);
canvasCtx.beginPath();
var sliceWidth = canvas.width * 1.0 / bufferLength;
var x = 0;
for (var i = 0; i < bufferLength; i++) {
var v = dataArray[i] / 128.0;
var 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();
}
loadVideo();
button { vertical-align: top }
<button disabled>record</button>