code: def on_position_changed(self, position):
          
          if not self._lyric:
              return
  
          pos = find_previous(position*1000 + 300, self._pos_list)
          if pos is not None and pos != self._pos:
              self.current_sentence = self._pos_s_map[pos]
              self._pos = pos
docs: bind position changed signal with this