code: def start_recording(self, output_file):
          
          if not self._started:
              raise Exception("Must start the video recorder first by calling .start()!")
          if self._recording:
              raise Exception("Cannot record a video while one is already recording!")
          self._recording = True
          self._cmd_q.put(('start', output_file))
docs: Starts recording to a given output video file.
  
          Parameters
          ----------
          output_file : :obj:`str`
              filename to write video to