播放时获得白屏

Question

我使用以下代码播放视频。但是当我运行该程序时，它会显示一个白色屏幕。请指教。我使用媒体播放器播放视频。当我使用视频观看它没有问题时播放：

    MediaPlayer mediaPlayer;
SurfaceView surfaceView;
SurfaceHolder surfaceHolder;
boolean pausing=false;
VideoView mVideoView;
Button play,stop;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_video);
    getWindow().setFormat(PixelFormat.UNKNOWN);
//      VideoView m=(VideoView)findViewById(R.id.videoView1);
//      String uriPath="android.resource://com.example.videoplayerthurs/"+R.raw.a;
//      Uri uri=Uri.parse(uriPath);
//      m.setVideoURI(uri);
//      m.requestFocus();
//      m.start();

     surfaceView = (SurfaceView) findViewById(R.id.surfaceView1);
     play=(Button)findViewById(R.id.button1);
     stop=(Button)findViewById(R.id.button2);
    play.setOnClickListener(new Button.OnClickListener(){

        @Override
        public void onClick(View view) {
            // TODO Auto-generated method stub

//              VideoView mVideoView=  (VideoView)findViewById(R.id.videoView1);
//              String       uriPath="android.resource://lk.sliit.androidvideoplayer/"+R.raw.a;
//              
//              Uri uri=Uri.parse(uriPath);
//              mVideoView.setVideoURI(uri);
//              mVideoView.requestFocus();
//              mVideoView.start();
            mediaPlayer=MediaPlayer.create(VideoActivity.this, R.raw.a);
            surfaceHolder=surfaceView.getHolder();
                    surfaceHolder.setType(SurfaceHolder.SURFACE_TYPE_PUSH_BUFFERS);
            mediaPlayer.setDisplay(surfaceHolder);
            mediaPlayer.start();
        }
    });

}