code: def _merge_filters(self) -> None:
          
          for opts in (["-filter:a", "-af"], ["-filter:v", "-vf"]):
              filter_list = []
              new_argv = []
              cmd_iter = iter(self._argv)
              for element in cmd_iter:
                  if element in opts:
                      filter_list.insert(0, next(cmd_iter))
                  else:
                      new_argv.append(element)
  
              # update argv if changes
              if filter_list:
                  new_argv.extend([opts[0], ",".join(filter_list)])
                  self._argv = new_argv.copy()
docs: Merge all filter config in command line.