webm-muxer实现带音乐的webm视频实例页面

CSS代码：

canvas,
video {
	width: 300px;
	height: 200px;
}

HTML代码：

<canvas id="canvas" width="600" height="400"></canvas>
<h4>音频素材</h4>
<p>
    <audio src="./win.mp3" controls preload="auto">
</p>

<p class="flex">
    <button id="generate">生成webM视频</button>
    <a id="download" download="muxer-with-audio.webm">下载</a>
</p>

<div class="view">
    <video id="video" width="600" height="400" controls></video>
    <p class="time">webm视频绘制时间：<output id="output1"></output>s，生成时间和播放一致（等音频流完整播放）：<output id="output2"></output>s</p>
</div>

JS代码：

// 页面内动画示意
handleDraw(document.getElementById('canvas'));

// 构造器，和音视频编码对象
var muxer = null;
var videoEncoder = null;
var audioEncoder = null;

// 结束编码
const endEncoding = async () => {
    await videoEncoder?.flush();
    await audioEncoder?.flush();
    muxer.finalize();

    let { buffer } = muxer.target;

    var blobUrl = URL.createObjectURL(new Blob([buffer]));
    video.src = blobUrl;
    download.href = blobUrl;

    videoEncoder = null;
    audioEncoder = null;
    muxer = null;
};

// 创建屏幕外 canvas
var canvas = document.createElement('canvas');
canvas.width = 600;
canvas.height = 400;

// 构造包装器
muxer = new WebMMuxer.Muxer({
    target: new WebMMuxer.ArrayBufferTarget(),
    video: {
        codec: 'V_VP9',
        width: canvas.width,
        height: canvas.height,
        frameRate: 30
    },
    audio: {
        codec: 'A_OPUS',
        sampleRate: 48000,
        numberOfChannels: 1
    },
    firstTimestampBehavior: 'offset'
});

// 音视频编码器，这里使用的是WebCodese API
videoEncoder = new VideoEncoder({
    output: (chunk, meta) => muxer.addVideoChunk(chunk, meta),
    error: e => console.error(e)
});
videoEncoder.configure({
    codec: 'vp09.00.10.08',
    width: canvas.width,
    height: canvas.height,
    bitrate: 1e6
});
// 音频的
audioEncoder = new AudioEncoder({
    output: (chunk, meta) => muxer.addAudioChunk(chunk, meta),
    error: e => console.error(e)
});
audioEncoder.configure({
    codec: 'opus',
    numberOfChannels: 1,
    sampleRate: 22050,
    bitrate: 64000
});

const myAudio = new Audio();
fetch(audio.src).then(res => {
    var reader = res.body.getReader();
    return reader.read().then(result => {
        return result;
    });
}).then(data => {
    var blob = new Blob([data.value], {
        type: 'audio/mp3'
    });
    var blobUrl = URL.createObjectURL(blob);

    // 创建音频对象
    myAudio.src = blobUrl;
    // 隐藏不可见
    myAudio.hidden = true;
    // 静音，避免干扰
    // myAudio.muted = true;
    // 在页面内，方便播放
    document.body.append(myAudio);
});

// 点击按钮的webM生成
generate.onclick = async function () {
    const audioTrack = myAudio.captureStream().getAudioTracks()[0];
    // MediaStreamTrackProcessor可以用来生成媒体帧流
    let trackProcessor = new MediaStreamTrackProcessor({
        track: audioTrack
    });

    // 音频播放，并实时抓取视频流
    // 交给webcodecs API进行编码
    myAudio.play();
    // 编码音频数据
    let consumer = new WritableStream({
        write(audioData) {
            // console.dir(audioData);
            if (!audioEncoder) {
                return;
            }
            audioEncoder.encode(audioData);
            audioData.close();
        }
    });
    trackProcessor.readable.pipeTo(consumer);

    // 编码视频数据
    var startTime = document.timeline.currentTime;
    var frameCounter = 0;
    // handleDraw源码可右键页面查看
    handleDraw(canvas, function () {
        let frame = new VideoFrame(canvas, {
            timestamp: (frameCounter * 1000 / 30) * 1000
        });

        // 把最后的帧作为视频的预览画面
        if (frameCounter == 30) {
            canvas.toBlob(function (blob) {
                video.poster = URL.createObjectURL(blob);
            }, 'image/jpeg', 0.95);
        }

        frameCounter++;
        videoEncoder.encode(frame, { keyFrame: frameCounter % 30 === 0 });
        frame.close();
    }, function () {
        // 预期结束时间
        // 由于音频和视频的编码时间不一致
        // 所以这里需要等待音频编码结束
        // 才能结束视频编码
        const timeUsed = document.timeline.currentTime - startTime;
        const timerActualEnd = frameCounter * 1000 / 30;

        setTimeout(function () {
            endEncoding();

            // 按钮提示还原
            generate.innerHTML = '生成完成';
        }, timerActualEnd - timeUsed);

        // 时间设置
        output1.innerHTML = Math.round(timeUsed / 10) / 100;
        output2.innerHTML = Math.round(timerActualEnd / 10) / 100;
    });

    // 一次性点击
    this.disabled = true;
    this.textContent = '生成中...';
};