在网页里面运行的JS程序，也是可以做到跨程序录屏的，比如录制QQ聊天界面、PPT展示等等，作为资深开发者，你可能会立即思考JS能力和权限的问题，它怎么可能逃出浏览器，访问到其他程序了呢？这仰仗WebRTC技术，在用户授权下可安全使用。
演示示例如下：
屏幕录屏：
加载的JS文件如下：
const videoElem = document.getElementById("video");
const logElem = document.getElementById("log");
const startElem = document.getElementById("start");
const stopElem = document.getElementById("stop");
// Options for getDisplayMedia()
var displayMediaOptions = {
video: {
cursor: "always"
},
audio: false
};
// Set event listeners for the start and stop buttons
startElem.addEventListener("click", function (evt) {
startCapture();
}, false);
stopElem.addEventListener("click", function (evt) {
stopCapture();
}, false);
console.log = msg => logElem.innerHTML += `${msg}<br>`;
console.error = msg => logElem.innerHTML += `<span class="error">${msg}</span><br>`;
console.warn = msg => logElem.innerHTML += `<span class="warn">${msg}<span><br>`;
console.info = msg => logElem.innerHTML += `<span class="info">${msg}</span><br>`;
async function startCapture() {
logElem.innerHTML = "";
try {
videoElem.srcObject = await navigator.mediaDevices.getDisplayMedia(displayMediaOptions);
dumpOptionsInfo();
} catch (err) {
console.error("Error: " + err);
}
}
function stopCapture(evt) {
let tracks = videoElem.srcObject.getTracks();
tracks.forEach(track => track.stop());
videoElem.srcObject = null;
}
function dumpOptionsInfo() {
const videoTrack = videoElem.srcObject.getVideoTracks()[0];
console.info("Track settings:");
console.info(JSON.stringify(videoTrack.getSettings(), null, 2));
console.info("Track constraints:");
console.info(JSON.stringify(videoTrack.getConstraints(), null, 2));
}
HTML内容如下：
<!DOCTYPE html>
<html>
<head>
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<meta charset="utf-8">
<meta name="robots" content="noindex, nofollow">
<style>
body {
padding: 0;
margin: 0;
}
svg:not(:root) {
display: block;
}
.playable-code {
background-color: #f4f7f8;
border: none;
border-left: 6px solid #558abb;
border-width: medium medium medium 6px;
color: #4d4e53;
height: 100px;
width: 90%;
padding: 10px 10px 0;
}
.playable-canvas {
border: 1px solid #4d4e53;
border-radius: 2px;
}
.playable-buttons {
text-align: right;
width: 90%;
padding: 5px 10px 5px 26px;
}
</style>
<style>
#video {
border: 1px solid #999;
width: 98%;
max-width: 860px;
}
.error {
color: red;
}
.warn {
color: orange;
}
.info {
color: darkgreen;
}
</style>
<title>使用屏幕捕获 API - simple_screen_capture - code sample</title>
</head>
<body>
<button id="start">Start Capture</button> <button id="stop">Stop Capture</button>
<video id="video" autoplay="autoplay"></video>
<br>
<strong>Log:</strong>
<br>
<pre id="log"></pre>
<script async src="capture.js"></script>
</body>
</html>
访问以上网页试一试
文件录制：
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>MediaCapture and Streams API</title>
<meta name="viewport" content="width=device-width">
</head>
<body>
<header>
<h1>媒体捕获、媒体记录器和流API</h1>
</header>
<main>
<p><button id="btnStart">开始录制</button><br/>
<button id="btnStop">停止录制</button></p>
<video controls></video>
<video id="vid2" controls></video>
</main>
<script>
let constraintObj = {
audio: false,
video: {
facingMode: "user",
width: { min: 640, ideal: 1280, max: 1920 },
height: { min: 480, ideal: 720, max: 1080 }
}
};
//getUserMedia旧浏览器兼容
if (navigator.mediaDevices === undefined) {
navigator.mediaDevices = {};
navigator.mediaDevices.getUserMedia = function(constraintObj) {
let getUserMedia = navigator.webkitGetUserMedia || navigator.mozGetUserMedia;
if (!getUserMedia) {
return Promise.reject(new Error('getUserMedia is not implemented in this browser'));
}
return new Promise(function(resolve, reject) {
getUserMedia.call(navigator, constraintObj, resolve, reject);
});
}
}else{
navigator.mediaDevices.enumerateDevices()
.then(devices => {
devices.forEach(device=>{
console.log(device.kind.toUpperCase(), device.label);
})
})
.catch(err=>{
console.log(err.name, err.message);
})
}
navigator.mediaDevices.getUserMedia(constraintObj)
.then(function(mediaStreamObj) {
let video = document.querySelector('video');
if ("srcObject" in video) {
video.srcObject = mediaStreamObj;
} else {
video.src = window.URL.createObjectURL(mediaStreamObj);
}
video.onloadedmetadata = function(ev) {
video.play();
};
let start = document.getElementById('btnStart');
let stop = document.getElementById('btnStop');
let vidSave = document.getElementById('vid2');
let mediaRecorder = new MediaRecorder(mediaStreamObj);
let chunks = [];
start.addEventListener('click', (ev)=>{
mediaRecorder.start();
console.log(mediaRecorder.state);
})
stop.addEventListener('click', (ev)=>{
mediaRecorder.stop();
console.log(mediaRecorder.state);
});
mediaRecorder.ondataavailable = function(ev) {
chunks.push(ev.data);
}
mediaRecorder.onstop = (ev)=>{
let blob = new Blob(chunks, { 'type' : 'video/mp4;' });
chunks = [];
let videoURL = window.URL.createObjectURL(blob);
vidSave.src = videoURL;
}
})
.catch(function(err) {
console.log(err.name, err.message);
});
</script>
</body>
</html>
该技术起源于谷歌，被用于基于网页的视频会议系统
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