code: def _put_output(self, output: Optional[str]) -> None:
          
          if output is None:
              self._argv.extend(["-f", "null", "-"])
              return
  
          output_cmd = shlex.split(str(output))
          if len(output_cmd) > 1:
              self._argv.extend(output_cmd)
          else:
              self._argv.append(output)
docs: Put output string to ffmpeg command.