Pixi.js实现闪电特效实例页面

JS代码：

// 使用 Webcodecs API 进行解码
const mp4url = './lightning2.mp4';
const mp4box = MP4Box.createFile();

// 这个是额外的处理方法，不需要关心里面的细节
const getExtradata = () => {
    // 生成VideoDecoder.configure需要的description信息
    const entry = mp4box.moov.traks[0].mdia.minf.stbl.stsd.entries[0];

    const box = entry.avcC ?? entry.hvcC ?? entry.vpcC;
    if (box != null) {
        const stream = new DataStream(
            undefined,
            0,
            DataStream.BIG_ENDIAN
        )
        box.write(stream)
         // slice()方法的作用是移除moov box的header信息
        return new Uint8Array(stream.buffer.slice(8))
    }
};

// 视频轨道，解码用
let videoTrack = null;
// let videoDuration = 0;
let videoDecoder = null;
// 这个就是最终解码出来的视频画面序列文件
const videoFrames = [];

let nbSampleTotal = 0;
let countSample = 0;

mp4box.onReady = function (info) {
    // 记住视频轨道信息，onSamples匹配的时候需要
    videoTrack = info.videoTracks[0];

    if (videoTrack != null) {
        mp4box.setExtractionOptions(videoTrack.id, 'video', { 
            nbSamples: 100 
        })
    }

    // 视频的宽度和高度
    const videoW = videoTrack.track_width;
    const videoH = videoTrack.track_height;

    // 设置视频解码器
    videoDecoder = new VideoDecoder({
        output: (videoFrame) => {
            createImageBitmap(videoFrame).then((img) => {
                videoFrames.push({
                    img,
                    duration: videoFrame.duration,
                    timestamp: videoFrame.timestamp,
                });
                videoFrame.close();
                
                // 判断何时结束，然后执行渲染
                if (videoFrames.length == nbSampleTotal) {
                    render();    
                }
            });
        },
        error: (err) => {
            console.error('videoDecoder错误：', err);
        },
    });

    nbSampleTotal = videoTrack.nb_samples;
    videoDecoder.configure({
        codec: videoTrack.codec,
        codedWidth: videoW,
        codedHeight: videoH,
        description: getExtradata(),
    });

    mp4box.start();
};

mp4box.onSamples = function (trackId, ref, samples) {
    // samples其实就是采用数据了
    if (videoTrack.id === trackId) {
        mp4box.stop();

        countSample += samples.length;

        for (const sample of samples) {
            const type = sample.is_sync ? 'key' : 'delta';

            const chunk = new EncodedVideoChunk({
                type,
                timestamp: sample.cts,
                duration: sample.duration,
                data: sample.data,
            });

            videoDecoder.decode(chunk);
        }

        if (countSample === nbSampleTotal) {
            videoDecoder.flush();
        }
    }
};

// 获取视频的arraybuffer数据
fetch(mp4url).then(res => res.arrayBuffer()).then(buffer => {
    // 因为文件较小，所以直接一次性写入
    // 如果文件较大，则需要res.body.getReader()创建reader对象，每次读取一部分数据
    // reader.read().then(({ done, value })
    buffer.fileStart = 0;
    mp4box.appendBuffer(buffer);
    mp4box.flush();
});


// 下面就是pixi对原图的绘制，以及解码后的视频帧了
const canvas = document.getElementById('canvas');
const view = canvas.transferControlToOffscreen()
// app 初始化
const viewWidth = 480;
const viewHeight = 480;
const app = new PIXI.Application({
    view,
    width: viewWidth,
    height: viewHeight,
    resolution: 1,
});
// 背景绘制
const background = PIXI.Sprite.from('./cloudy.jpg');

background.width = viewWidth;
background.height = viewHeight;
app.stage.addChild(background);

// 创建一个专门的imgContainer容器，用来不停地更新绘制
const imgContainer = new PIXI.Container();
// 并设置其混合模式为screen
// imgContainer.blendMode = PIXI.BLEND_MODES.SCREEN;
// 添加到舞台
app.stage.addChild(imgContainer);

// 以上就是解码过程，下面是将解码的videoFrames应用早canvas上，做特效展示
const render = () => {
    // 将img转为sprites，这样绘制时候省得多次创建了
    const spriteFrames = videoFrames.map(obj => {
        obj.sprite = PIXI.Sprite.from(obj.img);
        obj.sprite.x = 0;
        obj.sprite.y = 0;
        obj.sprite.width = viewWidth;
        obj.sprite.height = viewHeight;
        // 混合模式是滤色
        obj.sprite.blendMode = PIXI.BLEND_MODES.SCREEN
        
        return obj;
    });
    
    
    // 从videoFrames中取出数据，应用到canvas上
    let index = 0;
    // 绘制方法
    const draw = () => {
        const { sprite, duration } = spriteFrames[index];
        // 移除之前的
        imgContainer.removeChildren();
        // 添加新的
        imgContainer.addChild(sprite);

        // 开始下一帧绘制
        index++;

        if (index === videoFrames.length) {
            // 重新开始
            index = 0;
        }

        setTimeout(draw, duration);
    }

    draw();
}