docs: def set_sub_video_stream_type(self, format, callback=None):
          '''
          Set the stream fromat of sub stream.
          Supported format: (1) H264 : 0
                            (2) MotionJpeg 1
          '''
          params = {'format': format}
          return self.execute_command('setSubVideoStreamType',
                                          params, callback=callback)