private Button mPlay;
private YouTubePlayerView mTvRoyale;
private YouTubePlayer.OnInitializedListener onInitializedListener;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_principal);

mTvRoyale = (YouTubePlayerView) findViewById(R.id.tvRoyale);
    mPlay = (Button) findViewById(R.id.play);
    onInitializedListener = new YouTubePlayer.OnInitializedListener() {
        @Override
        public void onInitializationSuccess(YouTubePlayer.Provider provider, YouTubePlayer youTubePlayer, boolean b) {
            youTubePlayer.loadVideo("a4NT5iBFuZs");
        }

        @Override
        public void onInitializationFailure(YouTubePlayer.Provider provider, YouTubeInitializationResult youTubeInitializationResult) {

        }
    };
    mPlay.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mTvRoyale.initialize("AIzaS*************", onInitializedListener);
        }
    });