Simple WebRTC Demo

WebRTC is a peer to peer standard proposal from Google allowing browsers to connect directly and transfer information without a central server. This allows browsers to share raw data as well as audio/video.

This is a very simple video chat using WebRTC. I worked on it because I couldn't completely grok what was going on in apprtc.appspot.com - Google's canonical example. My version uses websockets instead of Google App Engine Channels, so you can see what the socket responses are doing, and I think the front end code is a bit simpler too.

Get It Running

git clone https://github.com/keithnorm/simple-webrtc-video-chat.git
cd simple-webrtc-vide-chat
npm install
./node_modules/coffee-script/bin/coffee app.coffee

Then open up two browser windows pointed to localhost:3002/room_name.

You should see something like this:

WebRTC in a nutshell

Firstly read through the article on HTML5 Rocks. Here are the steps to create a successful connection in high-level pseudo-code:

pc = new PeerConnection
ws = new WebSocket

// gets called when connection is complete
// this is when a remote peer can stream video 
// to your browser 
pc.onaddstream (event) ->
  remoteVid.src = event.stream

// local peer
pc.createOffer (description) ->
  pc.setLocalDescription(description)
  // over websockets
  ws.send description

ws.on 'create_offer', (data) ->
  // now this acts on a remote peer
  pc.setRemoteDescription(data)
  pc.createAnswer (description) ->
    pc.setLocalDescription(description)
    ws.send description

ws.on 'create_answer', (data) ->
  // back on local 
  pc.setRemoteDescription(data)

// called when handshake is complete
pc.onicecandidate = (event) ->
  // forward to remote
  ws.send event.candidate

ws.on 'ice_candidate', (data) ->
  pc.addIceCandidate(candidate)

So this song and dance is mainly complicated by the need to talk to the remote host via some transport method (websockets in this case). Check out public/javascripts/simple.js for an example of connecting two peers within the same browser window for an example of the PeerConnection API without the transport layer.

If you have any questions feel free to email me keithnorm@gmail.