let video = documnet.querySelector('video')
try {
  if ('srcObject' in video) {
      video.srcObject = null;
  } else {
    // Avoid using this in new browsers, as it is going away.
      video.src = null;
  }
} catch(e){
  console.log(e)
}

注意

• ​​src​​​置为​​''​​​无法清空​​video​​​ 且报错​​Uncaught TypeError: Failed to set the 'srcObject' property on 'HTMLMediaElement': Failed to convert value to 'MediaStream'.​​
• ​​src​​​置为​​null​​​可清空​​video​​​ 但报错​​Cannot set properties of null (setting 'srcObject')​​​会阻塞后续执行 - 解决办法：用​​try catch​​ 包裹