MediaRecorder

A new feature the MediaRecorder API is available in recent versions of Chrome and Firefox.

Here is the basic usage. It assumes that the "stream" variable is from a "getUserMedia" call:

	// This array will contain "chunks" of the video captured by the MediaRecorder
	var chunks = [];

	// Give the MediaRecorder the stream to record
	var mediaRecorder = new MediaRecorder(stream);

	// This is an event listener for the "stop" event on the MediaRecorder
	// Probably should write it:
	// mediaRecorder.addEventListener('stop', function(e) { ... });    
	mediaRecorder.onstop = function(e) {
		console.log("stop");

		// Create a new video element on the page
		var video = document.createElement('video');
		video.controls = true;
		
		// Create a blob - Binary Large Object of type video/webm
		var blob = new Blob(chunks, { 'type' : 'video/webm' });
		// Generate a URL for the blob
		var videoURL = window.URL.createObjectURL(blob);
		// Make the video element source point to that URL
		video.src = videoURL;
		
		// Put the video element on the page
		document.body.appendChild(video);
	};

	// Another callback/event listener - "dataavailable"
	mediaRecorder.ondataavailable = function(e) {
		console.log("data");
		// Whenever data is available from the MediaRecorder put it in the array
		chunks.push(e.data);
	};

	// Start the MediaRecorder
	mediaRecorder.start();

	// After 2 seconds, stop the MediaRecorder
	setTimeout(function() {
		mediaRecorder.stop();
	}, 2000);

Canvas as MediaRecorder Source

To do any of this, all that is required is to get a "stream" from the Canvas:

	var canvasStream = document.getElementById("thecanvas_id").captureStream();

More Information:
Record audio and video with MediaRecorder
Mozilla has a bit more documentation online
Record almost everything in the browser with MediaRecorder

Saving on Node.js with Socket.io

If you want to send the recorded video to a server for saving, it is as simple as emitting the "blob" of video to the server via a socket.

	mediaRecorder.onstop = function(e) {
		console.log("stop");

		var video = document.createElement('video');

		video.controls = true;
		var blob = new Blob(chunks, { 'type' : 'video/webm' });
		var videoURL = window.URL.createObjectURL(blob);
		video.src = videoURL;

		document.body.appendChild(video);

		// Send to the server
		socket.emit('video',blob);
	};

	socket.on('video', function(data){
		console.log(data);
		fs.writeFile(__dirname + '/x.webm', data, function(err){
			if (err) console.log(err);
			console.log("It's saved!")
		});
	});