摄像头在停止后几秒钟保持开启状态

我的相机有点怪。当我拍照时,它会立即关闭。但是,当我的组件卸载时,即使调用了完全相同的函数,在我的相机关闭之前可能需要10秒钟。我想它还是开着的,因为“照像机灯”还是开着的。以下是背后的逻辑:

class Webcam extends React.Component<Props> {
...
videoRef: any = React.createRef();

componentWillUnmount() {
  this.destroyCam();
}

destroyCam() {
    this.videoRef.srcObject.getTracks().forEach((track: MediaStream) => {
    track.stop();
  });
}

onShoot = () => {
  var timer = setInterval(() => {
    this.countdown--;
    if (this.countdown === 0) {
      this.destroyCam();
      clearInterval(timer);
    }
  }, 1000);
};

render() {
  return(
    ...
    <video ref={el => (this.videoRef = el)}/>
  )
}
}

就像我说的,当onShoot启动时,它会立即关闭摄像头。为什么在卸载组件时它不启动?