Signaling Server
                     |
         +-----------+-----------+
         |                       |
     Peer A                  Peer B
         |                       |
         +--- STUN/TURN Server --+
                     |
              Media Streams

// Get user media
const stream = await navigator.mediaDevices.getUserMedia({
  video: { width: 1280, height: 720 },
  audio: { echoCancellation: true, noiseSuppression: true }
});

// Create peer connection with STUN server
const pc = new RTCPeerConnection({
  iceServers: [
    { urls: 'stun:stun.l.google.com:19302' },
    { urls: 'turn:turn.example.com', username: 'user', credential: 'pass' }
  ]
});

// Add local tracks
stream.getTracks().forEach(track => pc.addTrack(track, stream));

// Handle ICE candidates
pc.onicecandidate = ({candidate}) => {
  if (candidate) sendToSignalingServer({type: 'candidate', candidate});
};

// Handle remote stream
pc.ontrack = ({streams}) => {
  remoteVideo.srcObject = streams[0];
};

// Create and send offer
const offer = await pc.createOffer();
await pc.setLocalDescription(offer);
sendToSignalingServer({type: 'offer', sdp: offer});

io.on('connection', socket => {
  socket.on('join-room', roomId => {
    socket.join(roomId);
    socket.to(roomId).emit('user-joined', socket.id);
  });

  socket.on('offer', ({to, sdp}) => {
    io.to(to).emit('offer', {from: socket.id, sdp});
  });

  socket.on('answer', ({to, sdp}) => {
    io.to(to).emit('answer', {from: socket.id, sdp});
  });

  socket.on('candidate', ({to, candidate}) => {
    io.to(to).emit('candidate', {from: socket.id, candidate});
  });
});

const screenStream = await navigator.mediaDevices.getDisplayMedia({
  video: { cursor: 'always' },
  audio: true  // System audio (browser support varies)
});

// Replace video track in existing connection
const videoSender = pc.getSenders().find(s => s.track?.kind === 'video');
await videoSender.replaceTrack(screenStream.getVideoTracks()[0]);