SFU vs MCU in WebRTC

1. Introduction

WebRTC (Web Real-Time Communication) allows audio, video, and data sharing between peers in a web browser. Two common architectures used in WebRTC applications are SFU (Selective Forwarding Unit) and MCU (Multipoint Control Unit). This lesson will explore the differences and use cases for SFU and MCU.

2. Key Definitions

3. What is SFU?

SFUs are designed to handle multiple streams efficiently. They selectively forward streams to connected clients, allowing each client to control which streams they want to receive. This is particularly useful in scenarios with a large number of participants.

const peerConnection = new RTCPeerConnection(configuration);
peerConnection.ontrack = (event) => {
    const remoteStream = event.streams[0];
    // Attach to video element
    document.getElementById('remoteVideo').srcObject = remoteStream;
};

4. What is MCU?

MCUs mix incoming media streams into a single stream that is sent to all participants. This can be useful for scenarios where a unified view of all streams is necessary, but it can also reduce the quality of the media streams.

const mixedStream = new MediaStream();
const audioTracks = [];
const videoTracks = [];

// Assume we have an array of local streams
streams.forEach(stream => {
    stream.getTracks().forEach(track => {
        if (track.kind === 'video') {
            videoTracks.push(track);
        } else if (track.kind === 'audio') {
            audioTracks.push(track);
        }
    });
});

// Now add them to the mixed stream
mixedStream.addTrack(...videoTracks);
mixedStream.addTrack(...audioTracks);

5. Comparison

• SFU allows for better scalability with lower bandwidth usage.
• MCU simplifies client-side implementation but may degrade quality.
• SFU supports adaptive bitrate streaming and allows for flexibility in stream management.
• MCU can be easier to implement for simple applications with limited participants.

6. Best Practices

1. Choose SFU for applications with many participants to optimize bandwidth.
2. Use MCU for applications needing a single mixed stream, like webinars.
3. Consider network conditions and participant capabilities when designing the architecture.
4. Test performance and latency in real-world scenarios to ensure optimal user experience.

7. FAQ