code: def _property_change_event_handler(self, signal, transport, *args):
          
          current_state = self.source.State
          if (self.state == 'connected' and current_state == 'playing'):
              self._acquire_media_transport(transport, 'r')
          elif (self.state == 'playing' and current_state == 'connected'):
              self._release_media_transport(transport, 'r')
          self.state = current_state
docs: Handler for property change event.  We catch certain state
          transitions in order to trigger media transport
          acquisition/release