n*igator.mediaDevices.getUserMedia({ video: true, audio: true })
  .then(stream => {
    // 成功获取流，可绑定到 <video> 标签预览
    videoElement.srcObject = stream;
    // 后续启动录制
  })
  .catch(err => {
    console.error("无法获取媒体设备：", err);
  });

let chunks = [];
const recorder = new MediaRecorder(stream);

recorder.ondata*ailable = event => {
  if (event.data.size > 0) {
    chunks.push(event.data);
  }
};

recorder.onstop = () => {
  const blob = new Blob(chunks, { type: 'video/webm' });
  const url = URL.createObjectURL(blob);
  const a = document.createElement('a');
  a.href = url;
  a.download = 'recording.webm';
  a.click();
  URL.revokeObjectURL(url);
  chunks = [];
};

// 开始录制
recorder.start();

// 停止录制（例如10秒后）
setTimeout(() => {
  recorder.stop();
}, 10000);

function getSupportedMimeTypes() {
  const types = ['video/webm', 'video/mp4', 'video/x-matroska'];
  return types.filter(type => MediaRecorder.isTypeSupported(type));
}

// 使用时选择第一个支持的
const options = { mimeType: getSupportedMimeTypes()[0] };
const recorder = new MediaRecorder(stream, options);