# File gstreamer/sample/media-type2.rb, line 82
  def get_decoder(mime)
    decoder = @decoders[mime]
    if decoder == nil
      factories = {
        'application/x-ogg' => 'vorbisfile',
        'audio/x-mp3' => 'mad',
        'audio/x-wav' => 'wavparse'
      }
      factory = factories[mime]
      return nil if factory == nil
      decoder = Gst::ElementFactory.make factory, 'decoder'
      @decoders[mime] = decoder if decoder != nil
    end
    return decoder
  end