Create mp4 video from set of images in the browser client side, using ffmpeg.js in worker thread

animation js

# Inspiration
* https://semisignal.com/tag/ffmpeg-js/
* https://github.com/antimatter15/whammy

ffmeg as worker can be found at https://github.com/Kagami/ffmpeg.js/

Final build can be obtained via `wget https://unpkg.com/ffmpeg.js@3.1.9001/ffmpeg-worker-mp4.js`

clock.html

<style>
* {font-family: sans-serif;}
</style>
<progress id="progress" value="0" max="60" min="0" style="width: 300px"></progress>
<br>
<canvas id="canvas" width="150" height="150"></canvas>
<video id="awesome" width="150" height="150" controls autoplay loop></video>
<br>
Status: <span id="status">Idle</span>
<a style="display:none" id="download" download="clock.webm">Download WebM</a>
<pre id="ffmsg"></pre>

<div id="images"></div>
<script>
// use requestanimation frame, woo!
(function() {
  var requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame ||
                              window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
  window.requestAnimationFrame = requestAnimationFrame;
})();

//stolen wholesale off mozilla's wiki


// the actual demo code, yaaay
var last_time = +new Date;
var progress = document.getElementById('progress');

const images = []

const $ = id => document.getElementById( id )

const worker = new Worker('/ffmpeg-worker-mp4.js')

function pad(n, width, z) {
  z = z || '0';
  n = n + '';
  return n.length >= width ? n : new Array(width - n.length + 1).join(z) + n;
}

function nextFrame(){
	progress.value++;
	var context = clock(last_time += 1000);

	const img = new Image()
	, mimeType = 'image/jpeg'

	const imgString = $('canvas').toDataURL(mimeType,1)

	const data = convertDataURIToBinary( imgString )

	images.push({
		name: `img${ pad( images.length, 3 ) }.jpeg`,
		data
	})

	img.src = imgString
	$('images').appendChild( img )

	if(progress.value / progress.max < 1){
		requestAnimationFrame(nextFrame);
		$('status').innerHTML = "Drawing Frames";
	}else{
		$('status').innerHTML = "Compiling Video";
		requestAnimationFrame(finalizeVideo); // well, should probably use settimeout instead
	}

}

// https://semisignal.com/tag/ffmpeg-js/
function convertDataURIToBinary(dataURI) {
    var base64 = dataURI.replace(/^data[^,]+,/,'');
    var raw = window.atob(base64);
    var rawLength = raw.length;

    var array = new Uint8Array(new ArrayBuffer(rawLength));
    for (i = 0; i < rawLength; i++) {
        array[i] = raw.charCodeAt(i);
    }
    return array;
};

//**blob to dataURL**
function blobToDataURL(blob, callback) {
	var a = new FileReader();
	a.onload = function(e) {callback(e.target.result);}
	a.readAsDataURL(blob);
}

let start_time

function finalizeVideo(){
	start_time = +new Date;

	const msgs = $('ffmsg')

	let messages = '';

	worker.onmessage = function(e) {
		var msg = e.data;
		switch (msg.type) {
			case "stdout":
			case "stderr":
				messages += msg.data + "\n";
				break;
			case "exit":
				console.log("Process exited with code " + msg.data);
				//worker.terminate();
				break;

			case 'done':
				const blob = new Blob([msg.data.MEMFS[0].data], {
					type: "video/mp4"
				});
				done( blob )

			break;
		}
		msgs.innerHTML = messages
	};

	// https://trac.ffmpeg.org/wiki/Slideshow
	// https://semisignal.com/tag/ffmpeg-js/
	worker.postMessage({
		type: 'run',
		TOTAL_MEMORY: 268435456,
		//arguments: 'ffmpeg -framerate 24 -i img%03d.jpeg output.mp4'.split(' '),
		arguments: ["-r", "20", "-i", "img%03d.jpeg", "-c:v", "libx264", "-crf", "1", "-vf", "scale=150:150", "-pix_fmt", "yuv420p", "-vb", "20M", "out.mp4"],
		//arguments: '-r 60 -i img%03d.jpeg -c:v libx264 -crf 1 -vf -pix_fmt yuv420p -vb 20M out.mp4'.split(' '),
		MEMFS: images
	});
	
	// Updated recommented arguments
	/*
			worker.postMessage({
			type: 'run',
			TOTAL_MEMORY: 268435456,
			arguments: [
				//"-r", opts.state.frameRate.toString(),
				"-framerate", opts.state.frameRate.toString(),
				"-frames:v", imgs.length.toString(),
				"-an", // disable sound
				"-i", "img%03d.jpeg",
				"-c:v", "libx264",
				"-crf", "17", // https://trac.ffmpeg.org/wiki/Encode/H.264
				"-filter:v",
				`scale=${w}:${h}`,
				"-pix_fmt", "yuv420p",
				"-b:v", "20M",
				"out.mp4"],
			MEMFS: imgs
		});*/

	/*video.compile(false, function(output){




		$('awesome').src = url; //toString converts it to a URL via Object URLs, falling back to DataURL
		$('download').style.display = '';
		$('download').href = url;


	});*/
}

function done(output) {

	const url = webkitURL.createObjectURL(output);

	var end_time = +new Date;
	$('status').innerHTML = "Compiled Video in " + (end_time - start_time) + "ms, file size: " + Math.ceil(output.size / 1024) + "KB";
	$('awesome').src = url; //toString converts it to a URL via Object URLs, falling back to DataURL
	$('download').style.display = '';
	$('download').href = url;
}

nextFrame();

function clock(time){
	var now = new Date();
	now.setTime(time);
	var ctx = document.getElementById('canvas').getContext('2d');
	ctx.save();
	ctx.fillStyle = 'white'
	ctx.fillRect(0,0,150,150); // videos cant handle transprency
	ctx.translate(75,75);
	ctx.scale(0.4,0.4);
	ctx.rotate(-Math.PI/2);
	ctx.strokeStyle = "black";
	ctx.fillStyle = "white";
	ctx.lineWidth = 8;
	ctx.lineCap = "round";

	// Hour marks
	ctx.save();
	for (var i=0;i<12;i++){
		ctx.beginPath();
		ctx.rotate(Math.PI/6);
		ctx.moveTo(100,0);
		ctx.lineTo(120,0);
		ctx.stroke();
	}
	ctx.restore();

	// Minute marks
	ctx.save();
	ctx.lineWidth = 5;
	for (i=0;i<60;i++){
		if (i%5!=0) {
			ctx.beginPath();
			ctx.moveTo(117,0);
			ctx.lineTo(120,0);
			ctx.stroke();
		}
		ctx.rotate(Math.PI/30);
	}
	ctx.restore();

	var sec = now.getSeconds();
	var min = now.getMinutes();
	var hr  = now.getHours();
	hr = hr>=12 ? hr-12 : hr;

	ctx.fillStyle = "black";

	// write Hours
	ctx.save();
	ctx.rotate( hr*(Math.PI/6) + (Math.PI/360)*min + (Math.PI/21600)*sec )
	ctx.lineWidth = 14;
	ctx.beginPath();
	ctx.moveTo(-20,0);
	ctx.lineTo(80,0);
	ctx.stroke();
	ctx.restore();

	// write Minutes
	ctx.save();
	ctx.rotate( (Math.PI/30)*min + (Math.PI/1800)*sec )
	ctx.lineWidth = 10;
	ctx.beginPath();
	ctx.moveTo(-28,0);
	ctx.lineTo(112,0);
	ctx.stroke();
	ctx.restore();

	// Write seconds
	ctx.save();
	ctx.rotate(sec * Math.PI/30);
	ctx.strokeStyle = "#D40000";
	ctx.fillStyle = "#D40000";
	ctx.lineWidth = 6;
	ctx.beginPath();
	ctx.moveTo(-30,0);
	ctx.lineTo(83,0);
	ctx.stroke();
	ctx.beginPath();
	ctx.arc(0,0,10,0,Math.PI*2,true);
	ctx.fill();
	ctx.beginPath();
	ctx.arc(95,0,10,0,Math.PI*2,true);
	ctx.stroke();
	ctx.fillStyle = "#555";
	ctx.arc(0,0,3,0,Math.PI*2,true);
	ctx.fill();
	ctx.restore();

	ctx.beginPath();
	ctx.lineWidth = 14;
	ctx.strokeStyle = '#325FA2';
	ctx.arc(0,0,142,0,Math.PI*2,true);
	ctx.stroke();

	ctx.restore();

	return ctx;
}
</script>