如何使用getUsermedia和mediaRecorder下载录像并给出视频规格？

navigator.mediaDevices.getUserMedia({ video: true, audio: true })
  .then(function(stream) {
    // 获取到音视频流后的处理逻辑
  })
  .catch(function(error) {
    // 处理获取音视频流失败的情况
  });

var mediaRecorder = new MediaRecorder(stream);

mediaRecorder.mimeType = 'video/webm'; // 设置录制的视频格式
mediaRecorder.videoBitsPerSecond = 2500000; // 设置视频的比特率
mediaRecorder.audioBitsPerSecond = 128000; // 设置音频的比特率

var chunks = [];
mediaRecorder.addEventListener('dataavailable', function(event) {
  chunks.push(event.data);
});

mediaRecorder.addEventListener('stop', function() {
  var blob = new Blob(chunks, { type: mediaRecorder.mimeType });
  var url = URL.createObjectURL(blob);
  
  // 创建一个下载链接
  var a = document.createElement('a');
  a.href = url;
  a.download = 'recorded-video.webm';
  document.body.appendChild(a);
  a.click();
  document.body.removeChild(a);
});