old_contents: import multiprocessing
  
  from mopidy.mixers import BaseMixer
  from mopidy.utils.process import pickle_connection
  
  class GStreamerSoftwareMixer(BaseMixer):
      """Mixer which uses GStreamer to control volume in software."""
  
      def __init__(self, *args, **kwargs):
          super(GStreamerSoftwareMixer, self).__init__(*args, **kwargs)
  
      def _get_volume(self):
          my_end, other_end = multiprocessing.Pipe()
          self.backend.output_queue.put({
              'command': 'get_volume',
              'reply_to': pickle_connection(other_end),
          })
          my_end.poll(None)
          return my_end.recv()
  
      def _set_volume(self, volume):
          self.backend.output_queue.put({
              'command': 'set_volume',
              'volume': volume,
          })
  
new_contents: from mopidy.mixers import BaseMixer
  
  class GStreamerSoftwareMixer(BaseMixer):
      """Mixer which uses GStreamer to control volume in software."""
  
      def __init__(self, *args, **kwargs):
          super(GStreamerSoftwareMixer, self).__init__(*args, **kwargs)
  
      def _get_volume(self):
          return self.backend.output.get_volume()
  
      def _set_volume(self, volume):
          self.backend.output.set_volume(volume)
  
subject: Update GStreamer software mixer to use new output API