code: private void sendAction(Context context, String action) {
          Intent intent = new Intent(context, PlaybackService.class);
          intent.setAction(action);
          LocalBroadcastManager.getInstance(context).sendBroadcast(intent);
      }
docs: Propagate lock screen event to the player.
  
  @param context context used to start service.
  @param action  action to send.