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)