How to sharing accomplish screen using WebRTC

1. What is WebRTC?

WebRTC (Web Real-Time Communication) is an open-source project designed to enable real-time communication directly within web browsers through simple APIs, without requiring any plugins. WebRTC supports the transmission of video, audio, and arbitrary data, making it suitable for applications such as browser-based video conferencing and file sharing.

2. How Screen Sharing Works in WebRTC?

Implementing screen sharing in WebRTC typically involves the following main steps:

a. Obtain Screen Capture Permission

First, obtain the user's screen capture permission. This is achieved by calling the navigator.mediaDevices.getDisplayMedia() method, which displays a prompt for the user to select the screen or window to share.

javascript
async function getScreenStream() {
    try {
        const screenStream = await navigator.mediaDevices.getDisplayMedia({
            video: true
        });
        return screenStream;
    } catch (error) {
        console.error("Error: Unable to access screen", error);
    }
}

b. Create an RTCPeerConnection

Create an RTCPeerConnection object, which handles the transmission of the screen-sharing data stream.

javascript
const peerConnection = new RTCPeerConnection();

c. Add the Captured Screen Data Stream to the Connection

Add the media stream obtained from getDisplayMedia() to the RTCPeerConnection.

javascript
const screenStream = await getScreenStream();
peerConnection.addTrack(screenStream.getVideoTracks()[0], screenStream);

d. Exchange Information via a Signaling Server

Use a signaling mechanism (such as WebSocket or Socket.io) between the initiator and receiver to exchange necessary information (such as SDP offers/answers and ICE candidates) to establish and maintain the connection.

javascript
// Send offer
const offer = await peerConnection.createOffer();
await peerConnection.setLocalDescription(offer);
signalServer.send({type: "offer", sdp: offer});

// Receive answer
signalServer.on("message", async message => {
    if (message.type === "answer") {
        await peerConnection.setRemoteDescription(new RTCSessionDescription(message.sdp));
    }
});

e. Establish the Connection and Start Screen Sharing

Once the SDP and ICE candidates are exchanged, the connection is established, and screen sharing begins.

3. Practical Application Example

In one of my projects, we needed to implement a virtual classroom where teachers can share their screens with students. Using WebRTC's screen-sharing feature, teachers can seamlessly share their screens among students in different geographical locations. We obtained the teacher's screen stream using getDisplayMedia() and sent it to each student via RTCPeerConnection. Additionally, we used Socket.io as the signaling mechanism to exchange SDP information and ICE candidates. This solution significantly improved classroom interactivity and students' learning efficiency.

Summary

WebRTC provides a powerful and flexible approach to implementing screen sharing without relying on external plugins or dedicated software. Through simple API calls, it enables direct, real-time communication between browsers, which has broad applications in remote work, online education, and collaborative work.