// 开始屏幕录制
async startRecording() {
  const stream = await invokeGetDisplayMedia();
  if(!stream) return;
  let videoIndex = 0;  //录屏分片序号
  let dataArr = [];  // 本地看视频
  let mediaRecorderTimer = null;  // 定时上传录屏文件
  const mime = MediaRecorder.isTypeSupported("video/webm;codecs=h264")
    ? "video/webm;codecs=h264"
    : "video/webm";
  const mediaRecorder = new MediaRecorder(stream, { mimeType: mime });
  mediaRecorder.ondataavailable = event => {
    if (event.data && event.data.size > 0) {
      dataArr.push(event.data); 
      if(mediaRecorder.state === 'inactive') {  // 判断是否停止录制
        // to do
        let mediaBlob = new Blob(dataArr, { type: "video/webm" });
        document.getElementById("recVideo").src = window.URL.createObjectURL(mediaBlob);
      }
      const formData = new FormData();
      formData.append("videoIndex", videoIndex)
      formData.append("file", event.data)
      request({
        url: '/upload',
        method: 'post',
        headers: { 'Content-Type': 'multipart/form-data' },
        responseType: 'blob',
        data: formData,
        timeout: 1000 * 60 * 10,
      })
      videoIndex++;
    }
  };

  // 初始化开始
  mediaRecorder.start();

  // 监听停止录屏
  mediaRecorder.onstop = () => {
    clearInterval(mediaRecorderTimer);
   mediaRecorderTimer = null;
  } 

  // 设置定时上传录屏分片
 mediaRecorderTimer = setInterval(() => {
    if (mediaRecorder) {
      mediaRecorder.requestData();
    }
  }, 10000); // 每10000毫秒请求一次
}

// 获取屏幕录制授权
async invokeGetDisplayMedia() {
  return new Promise(async (resolve, reject) => {
    if (navigator.mediaDevices && navigator.mediaDevices.getUserMedia) {
      const displaymediastreamconstraints = {
        video: true,
        audio: {
          echoCancellation: true,
          noiseSuppression: true,
          sampleRate: 44100,
        },
        screen: true,
        preferCurrentTab: true,
      };
      const stream = await navigator.mediaDevices.getDisplayMedia(
        displaymediastreamconstraints
      );
      if (stream) {
        resolve(stream);
      } else {
        reject(false);
      }
    } else {
      console.log('浏览器不支持getUserMedia');
      reject(false);
    }
  });
}

注意
让后端拿到全部的视频流文件再去转成视频，如果拿到第一个就转，那么后面的切片文件会缺少头部数据，视频将无法正常拼接。