private static final class OnRoutingChangedListenerApi24 {

    private final AudioTrack audioTrack;
    private final AudioCapabilitiesReceiver capabilitiesReceiver;

    @Nullable private OnRoutingChangedListener listener;

    public OnRoutingChangedListenerApi24(
        AudioTrack audioTrack, AudioCapabilitiesReceiver capabilitiesReceiver) {
      this.audioTrack = audioTrack;
      this.capabilitiesReceiver = capabilitiesReceiver;
      this.listener = this::onRoutingChanged;
      // the following line gets handler of ExoPlayer:Playback thread
      Handler handler = new Handler(Looper.myLooper());
      audioTrack.addOnRoutingChangedListener(listener, handler);
    }

    public void release() {
      audioTrack.removeOnRoutingChangedListener(checkNotNull(listener));
      listener = null;
    }

    private void onRoutingChanged(AudioRouting router) {
      if (listener == null) {
        // Stale event.
        return;
      }
      @Nullable AudioDeviceInfo routedDevice = router.getRoutedDevice();
      if (routedDevice != null) {
        capabilitiesReceiver.setRoutedDevice(routedDevice);
      }
    }
  }

    public OnRoutingChangedListenerApi24(
        AudioTrack audioTrack, AudioCapabilitiesReceiver capabilitiesReceiver) {
      this.audioTrack = audioTrack;
      this.capabilitiesReceiver = capabilitiesReceiver;
      this.listener = this::onRoutingChanged;
      if (routingChangedHandlerThread == null) {
        routingChangedHandlerThread =
            new HandlerThread("ExoPlayer:RoutingChangedHandler", Process.THREAD_PRIORITY_AUDIO);
        routingChangedHandlerThread.start();
      }
      Handler handler = new Handler(routingChangedHandlerThread.getLooper());
      audioTrack.addOnRoutingChangedListener(listener, handler);
    }