Image doesn't show on top of a MPMoviePlayerController

Question

I use MPMoviePlayerViewController to play video in my ios app. I want to show some ads(pictures) above the player when the video is paused. I used method here.

However, nothing shows up when I pause the video, my code is below:

#import "ViewController.h"
#import <MediaPlayer/MediaPlayer.h>

@interface ViewController ()
{
@private
    MPMoviePlayerController *player;
    UIImageView *image;

}

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    UIButton * button = [UIButton buttonWithType:UIButtonTypeRoundedRect];
    button.frame = CGRectMake(100, 100, 100, 50);
    [button setTitle:@"play" forState:UIControlStateNormal];
    [button addTarget:self action:@selector(buttonClick) forControlEvents:UIControlEventTouchUpInside];
    [self.view addSubview:button];


    NSURL *videoStreamURL = [NSURL URLWithString:@"http://devimages.apple.com/iphone/samples/bipbop/bipbopall.m3u8"];
    player = [[MPMoviePlayerController alloc]initWithContentURL:videoStreamURL];
    player.view.frame = CGRectMake(0, 0, self.view.frame.size.width, 320);

    [[NSNotificationCenter defaultCenter] addObserver:self
                                             selector:@selector(playbackStateChanged)
                                                 name:MPMoviePlayerPlaybackStateDidChangeNotification object:nil];

}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
}

-(void) buttonClick{
    [self.view addSubview:player.view];
    [player play];
}

- (void)playbackStateChanged{
    switch (player.playbackState) {
        case MPMoviePlaybackStatePaused:
            //add ads
            image = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"ad.jpg"]];
            image.frame = CGRectMake(0, 0, self.view.frame.size.width, 320);
            [player.view addSubview:image];
            break;

        default:
            break;
    }
}
@end

Can anybody help me? Thanks!