`

- (AVCaptureDevice *)findDeviceForPosition:(AVCaptureDevicePosition)position {
  NSArray<AVCaptureDevice *> *captureDevices = [RTCCameraVideoCapturer captureDevices];
  for (AVCaptureDevice *device in captureDevices) {
    if (device.position == position) {
      return device;
    }
  }
    return captureDevices[0];
}
`

这个函数内的代码是这样的，崩溃的原因只能是captureDevices为空，也就是说没有获取到摄像头。有可能是没有摄像头或者没有允许权限