相关API简介
在前面的章节中,已经对WebRTC相关的重要知识点进行了介绍,包括涉及的网络协议、会话描述协议、如何进行网络穿透等,剩下的就是WebRTC的API了。
WebRTC通信相关的API非常多,主要完成了如下功能:
- 信令交换
- 通信候选地址交换
- 音视频采集
- 音视频发送、接收
相关API太多,为避免篇幅过长,文中部分采用了伪代码进行讲解。详细代码参考文章末尾,也可以在笔者的Github上找到,有问题欢迎留言交流。
信令交换
信令交换是WebRTC通信中的关键环节,交换的信息包括编解码器、网络协议、候选地址等。对于如何进行信令交换,WebRTC并没有明确说明,而是交给应用自己来决定,比如可以采用WebSocket。
发送方伪代码如下:
const pc = new RTCPeerConnection(iceConfig);
const offer = await pc.createOffer();
await pc.setLocalDescription(offer);
sendToPeerViaSignalingServer(SIGNALING_OFFER,offer); // 发送方发送信令消息
接收方伪代码如下:
const pc = new RTCPeerConnection(iceConfig);
await pc.setRemoteDescription(offer);
const answer = await pc.createAnswer();
await pc.setLocalDescription(answer);
sendToPeerViaSignalingServer(SIGNALING_ANSWER,answer); // 接收方发送信令消息
候选地址交换服务
当本地设置了会话描述信息,并添加了媒体流的情况下,ICE框架就会开始收集候选地址。两边收集到候选地址后,需要交换候选地址,并从中知道合适的候选地址对。
候选地址的交换,同样采用前面提到的信令服务,伪代码如下:
// 设置本地会话描述信息
const localPeer = new RTCPeerConnection(iceConfig);
const offer = await pc.createOffer();
await localPeer.setLocalDescription(offer);
// 本地采集音视频
const localVideo = document.getElementById('local-video');
const mediaStream = await navigator.mediaDevices.getUserMedia({
video: true,audio: true
});
localVideo.srcObject = mediaStream;
// 添加音视频流
mediaStream.getTracks().forEach(track => {
localPeer.addTrack(track,mediaStream);
});
// 交换候选地址
localPeer.onicecandidate = function(evt) {
if (evt.candidate) {
sendToPeerViaSignalingServer(SIGNALING_CANDIDATE,evt.candidate);
}
}
音视频采集
可以使用浏览器提供的getUserMedia接口,采集本地的音视频。
const localVideo = document.getElementById('local-video');
const mediaStream = await navigator.mediaDevices.getUserMedia({
video: true,audio: true
});
localVideo.srcObject = mediaStream;
音视频发送、接收
将采集到的音视频轨道,通过addTrack进行添加,发送给远端。
mediaStream.getTracks().forEach(track => {
localPeer.addTrack(track,mediaStream);
});
远端可以通过监听ontrack来监听音视频的到达,并进行播放。
remotePeer.ontrack = function(evt) {
const remoteVideo = document.getElementById('remote-video');
remoteVideo.srcObject = evt.streams[0];
}
完整代码
包含两部分:客户端代码、服务端代码。
1、客户端代码
const socket = io.connect('http://localhost:3000');
const CLIENT_RTC_EVENT = 'CLIENT_RTC_EVENT';
const SERVER_RTC_EVENT = 'SERVER_RTC_EVENT';
const CLIENT_USER_EVENT = 'CLIENT_USER_EVENT';
const SERVER_USER_EVENT = 'SERVER_USER_EVENT';
const CLIENT_USER_EVENT_LOGIN = 'CLIENT_USER_EVENT_LOGIN'; // 登录
const SERVER_USER_EVENT_UPDATE_USERS = 'SERVER_USER_EVENT_UPDATE_USERS';
const SIGNALING_OFFER = 'SIGNALING_OFFER';
const SIGNALING_ANSWER = 'SIGNALING_ANSWER';
const SIGNALING_CANDIDATE = 'SIGNALING_CANDIDATE';
let remoteUser = ''; // 远端用户
let localUser = ''; // 本地登录用户
function log(msg) {
console.log(`[client] ${msg}`);
}
socket.on('connect',function() {
log('ws connect.');
});
socket.on('connect_error',function() {
log('ws connect_error.');
});
socket.on('error',function(errorMessage) {
log('ws error,' + errorMessage);
});
socket.on(SERVER_USER_EVENT,function(msg) {
const type = msg.type;
const payload = msg.payload;
switch(type) {
case SERVER_USER_EVENT_UPDATE_USERS:
updateUserList(payload);
break;
}
log(`[${SERVER_USER_EVENT}] [${type}],${jsON.stringify(msg)}`);
});
socket.on(SERVER_RTC_EVENT,function(msg) {
const {type} = msg;
switch(type) {
case SIGNALING_OFFER:
handleReceiveOffer(msg);
break;
case SIGNALING_ANSWER:
handleReceiveAnswer(msg);
break;
case SIGNALING_CANDIDATE:
handleReceiveCandidate(msg);
break;
}
});
async function handleReceiveOffer(msg) {
log(`receive remote description from ${msg.payload.from}`);
// 设置远端描述
const remoteDescription = new RTCSessionDescription(msg.payload.sdp);
remoteUser = msg.payload.from;
createPeerConnection();
await pc.setRemoteDescription(remoteDescription); // TODO 错误处理
// 本地音视频采集
const localVideo = document.getElementById('local-video');
const mediaStream = await navigator.mediaDevices.getUserMedia({ video: true,audio: true });
localVideo.srcObject = mediaStream;
mediaStream.getTracks().forEach(track => {
pc.addTrack(track,mediaStream);
// pc.addTransceiver(track,{streams: [mediaStream]}); // 这个也可以
});
// pc.addStream(mediaStream); // 目前这个也可以,不过接口后续会废弃
const answer = await pc.createAnswer(); // TODO 错误处理
await pc.setLocalDescription(answer);
sendRTCEvent({
type: SIGNALING_ANSWER,payload: {
sdp: answer,from: localUser,target: remoteUser
}
});
}
async function handleReceiveAnswer(msg) {
log(`receive remote answer from ${msg.payload.from}`);
const remoteDescription = new RTCSessionDescription(msg.payload.sdp);
remoteUser = msg.payload.from;
await pc.setRemoteDescription(remoteDescription); // TODO 错误处理
}
async function handleReceiveCandidate(msg){
log(`receive candidate from ${msg.payload.from}`);
await pc.addIceCandidate(msg.payload.candidate); // TODO 错误处理
}
/**
* 发送用户相关消息给服务器
* @param {Object} msg 格式如 { type: 'xx',payload: {} }
*/
function sendUserEvent(msg) {
socket.emit(CLIENT_USER_EVENT,jsON.stringify(msg));
}
/**
* 发送RTC相关消息给服务器
* @param {Object} msg 格式如{ type: 'xx',payload: {} }
*/
function sendRTCEvent(msg) {
socket.emit(CLIENT_RTC_EVENT,JSON.stringify(msg));
}
let pc = null;
/**
* 邀请用户加入视频聊天
* 1、本地启动视频采集
* 2、交换信令
*/
async function startVideoTalk() {
// 开启本地视频
const localVideo = document.getElementById('local-video');
const mediaStream = await navigator.mediaDevices.getUserMedia({
video: true,audio: true
});
localVideo.srcObject = mediaStream;
// 创建 peerConnection
createPeerConnection();
// 将媒体流添加到webrtc的音视频收发器
mediaStream.getTracks().forEach(track => {
pc.addTrack(track,{streams: [mediaStream]});
});
// pc.addStream(mediaStream); // 目前这个也可以,不过接口后续会废弃
}
function createPeerConnection() {
const iceConfig = {"iceServers": [
{url: 'stun:stun.ekiga.net'},{url: 'turn:turnserver.com',username: 'user',credential: 'pass'}
]};
pc = new RTCPeerConnection(iceConfig);
pc.onnegotiationneeded = onnegotiationneeded;
pc.onicecandidate = onicecandidate;
pc.onicegatheringstatechange = onicegatheringstatechange;
pc.oniceconnectionstatechange = oniceconnectionstatechange;
pc.onsignalingstatechange = onsignalingstatechange;
pc.ontrack = ontrack;
return pc;
}
async function onnegotiationneeded() {
log(`onnegotiationneeded.`);
const offer = await pc.createOffer();
await pc.setLocalDescription(offer); // TODO 错误处理
sendRTCEvent({
type: SIGNALING_OFFER,payload: {
from: localUser,target: remoteUser,sdp: pc.localDescription // TODO 直接用offer?
}
});
}
function onicecandidate(evt) {
if (evt.candidate) {
log(`onicecandidate.`);
sendRTCEvent({
type: SIGNALING_CANDIDATE,payload: {
from: localUser,candidate: evt.candidate
}
});
}
}
function onicegatheringstatechange(evt) {
log(`onicegatheringstatechange,pc.iceGatheringState is ${pc.iceGatheringState}.`);
}
function oniceconnectionstatechange(evt) {
log(`oniceconnectionstatechange,pc.iceConnectionState is ${pc.iceConnectionState}.`);
}
function onsignalingstatechange(evt) {
log(`onsignalingstatechange,pc.signalingstate is ${pc.signalingstate}.`);
}
// 调用 pc.addTrack(track,mediaStream),remote peer的 onTrack 会触发两次
// 实际上两次触发时,evt.streams[0] 指向同一个mediaStream引用
// 这个行为有点奇怪,github issue 也有提到 https://github.com/meetecho/janus-gateway/issues/1313
let stream;
function ontrack(evt) {
// if (!stream) {
// stream = evt.streams[0];
// } else {
// console.log(`${stream === evt.streams[0]}`); // 这里为true
// }
log(`ontrack.`);
const remoteVideo = document.getElementById(
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