private void preparePlayer() {

    if (player == null) {
      String userAgent = Util.getUserAgent(this, "ExoPlayerDemo");
      player =
          new DemoPlayer(
              new HlsRendererBuilder(
                  this, userAgent, VIDEO_URL.toString(), null, audioCapabilities));
      player.addListener(this);
      player.seekTo(playerPosition);
      playerNeedsPrepare = true;
      mediaController.setMediaPlayer(player.getPlayerControl());
      mediaController.setEnabled(true);
    }
    if (playerNeedsPrepare) {
      player.prepare();
      playerNeedsPrepare = false;
      updateButtonVisibilities();
    }
    player.setSurface(surfaceView.getHolder().getSurface());
    player.setPlayWhenReady(true);
  }
 @Override
 public void surfaceCreated(SurfaceHolder holder) {
   if (player != null) {
     player.setSurface(holder.getSurface());
   }
 }