code: private void initPlaybackStateBuilder() {
          mStateBuilder = new PlaybackStateCompat.Builder();
          mStateBuilder.setActions(
                  PlaybackStateCompat.ACTION_PLAY
                          | PlaybackStateCompat.ACTION_PAUSE
                          | PlaybackStateCompat.ACTION_PLAY_PAUSE
                          | PlaybackStateCompat.ACTION_SKIP_TO_NEXT
                          | PlaybackStateCompat.ACTION_SKIP_TO_PREVIOUS
          );
      }
docs: Initialize the playback state builder with supported actions.