code: def iter_duration(self, iter_trigger):
          
          print
          process_info = ProcessInfo(self.frame_count, use_last_rates=4)
          start_time = time.time()
          next_status = start_time + 0.25
  
          old_pos = next(iter_trigger)
          for pos in iter_trigger:
              duration = pos - old_pos
  #             log.log(5, "Duration: %s" % duration)
              yield duration
              old_pos = pos
  
              if time.time() > next_status:
                  next_status = time.time() + 1
                  self._print_status(process_info)
  
          self._print_status(process_info)
          print
docs: yield the duration of two frames in a row.