我有一个动画画布,我想将其转换为 mp4。我正在使用 MediaRecorder 捕获屏幕,然后转换该 Blob。我了解到 MediaRecorder 不允许以 mp4 格式录制,因此我被迫在 webm 中获取画布。这是我尝试过的:
<canvas id="canvas"></canvas>
var recordedChunks = [];
var time = 0;
var canvas = document.getElementById("canvas");
return new Promise(function (res, rej) {
var stream = canvas.captureStream(60);
mediaRecorder = new MediaRecorder(stream, {
mimeType: "video/webm; codecs=vp9"
});
mediaRecorder.start(time);
mediaRecorder.ondataavailable = function (e) {
recordedChunks.push(event.data);
if (mediaRecorder.state === 'recording') {
mediaRecorder.stop();
}
}
mediaRecorder.onstop = function (event) {
var blob = new Blob(recordedChunks, {
"type": "video/webm"
});
var url = URL.createObjectURL(blob);
res(url);
var xhr = new XMLHttpRequest;
xhr.responseType = 'blob';
xhr.onload = function() {
var recoveredBlob = xhr.response;
var reader = new FileReader;
reader.onload = function() {
var blobAsDataUrl = reader.result;
document.getElementById("my-video").setAttribute("src", blobAsDataUrl);
};
reader.readAsDataURL(recoveredBlob);
};
xhr.open('GET', url);
xhr.send();
}
});
任何解决方案都受到高度赞赏。
使用 ffmpeg.wasm 进行转码的快速演示:
const { createFFmpeg } = FFmpeg;
const ffmpeg = createFFmpeg({
log: true
});
const transcode = async (webcamData) => {
const message = document.getElementById('message');
const name = 'record.webm';
await ffmpeg.load();
message.innerHTML = 'Start transcoding';
await ffmpeg.write(name, webcamData);
await ffmpeg.transcode(name, 'output.mp4');
message.innerHTML = 'Complete transcoding';
const data = ffmpeg.read('output.mp4');
const video = document.getElementById('output-video');
video.src = URL.createObjectURL(new Blob([data.buffer], { type: 'video/mp4' }));
dl.href = video.src;
dl.innerHTML = "download mp4"
}
fn().then(async ({url, blob})=>{
transcode(new Uint8Array(await (blob).arrayBuffer()));
})
function fn() {
var recordedChunks = [];
var time = 0;
var canvas = document.getElementById("canvas");
return new Promise(function (res, rej) {
var stream = canvas.captureStream(60);
mediaRecorder = new MediaRecorder(stream, {
mimeType: "video/webm; codecs=vp9"
});
mediaRecorder.start(time);
mediaRecorder.ondataavailable = function (e) {
recordedChunks.push(event.data);
// for demo, removed stop() call to capture more than one frame
}
mediaRecorder.onstop = function (event) {
var blob = new Blob(recordedChunks, {
"type": "video/webm"
});
var url = URL.createObjectURL(blob);
res({url, blob}); // resolve both blob and url in an object
myVideo.src = url;
// removed data url conversion for brevity
}
// for demo, draw random lines and then stop recording
var i = 0,
tid = setInterval(()=>{
if(i++ > 20) { // draw 20 lines
clearInterval(tid);
mediaRecorder.stop();
}
let canvas = document.querySelector("canvas");
let cx = canvas.getContext("2d");
cx.beginPath();
cx.strokeStyle = 'green';
cx.moveTo(Math.random()*100, Math.random()*100);
cx.lineTo(Math.random()*100, Math.random()*100);
cx.stroke();
},200)
});
}
<script src="https://unpkg.com/@ffmpeg/[email protected]/dist/ffmpeg.min.js"></script>
<canvas id="canvas" style="height:100px;width:100px"></canvas>
<video id="myVideo" controls="controls"></video>
<video id="output-video" controls="controls"></video>
<a id="dl" href="" download="download.mp4"></a>
<div id="message"></div>
提供的 ffmpeg.wasm 解决方案的替代方案是使用 WebCodecs API。我整理了一个教程 如何使用 WebCodecs API 将 HTML Canvas 保存到 Mp4
好处包括不必下载所有 ffmpeg 以及能够比实时更快地渲染视频。