AVPlayer 不会在 iOS9 中播放来自 url 的视频

我试图在 UIView 中嵌入 AVPlayer 并从 url 播放 mp4 视频文件。问题是我只收到黑色空白视图（参见屏幕截图）

在以前的 iOS 版本中，它对我有用，但自从升级到 iOS9 后，我遇到了这个问题。

我的 .h 文件如下所示：

@interface ViewController : UIViewController
@property (strong, nonatomic) IBOutlet UIView *viewPlayerContainer;

而在我的实现文件中，我有以下内容：

@import AVFoundation;
@import AVKit;

@interface ViewController ()

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];

    AVPlayerViewController *playerViewController = [[AVPlayerViewController alloc] init];

    NSURL *url = [NSURL URLWithString:@"http://techslides.com/demos/sample-videos/small.mp4"];

    AVURLAsset *asset = [AVURLAsset assetWithURL: url];
    AVPlayerItem *item = [AVPlayerItem playerItemWithAsset: asset];

    AVPlayer * player = [[AVPlayer alloc] initWithPlayerItem: item];

    [playerViewController.view setFrame:CGRectMake(0, 0, _viewPlayerContainer.bounds.size.width, _viewPlayerContainer.bounds.size.width)];

    playerViewController.showsPlaybackControls = NO;

    [_viewPlayerContainer addSubview:playerViewController.view];


    [player play];


}

我在这里错过了什么吗？

提前致谢！

@implementation ViewController{
    AVPlayerViewController *playerViewController;
}

- (void)viewDidLoad {
    [super viewDidLoad];
     playerViewController = [[AVPlayerViewController alloc] init];
}

- (IBAction)playVideo:(id)sender {
    NSURL *url = [NSURL URLWithString:@"http://techslides.com/demos/sample-videos/small.mp4"];

    AVURLAsset *asset = [AVURLAsset assetWithURL: url];
    AVPlayerItem *item = [AVPlayerItem playerItemWithAsset: asset];

    AVPlayer * player = [[AVPlayer alloc] initWithPlayerItem: item];
    playerViewController.player = player;
    [playerViewController.view setFrame:CGRectMake(0, 0, self.view.bounds.size.width, self.view.bounds.size.width)];

    playerViewController.showsPlaybackControls = YES;

    [self.view addSubview:playerViewController.view];

    [player play];
}