ios – 无法观察AVPlayerItem的@“status”键

我正在尝试从URL播放流,但这是一个问题. ObserveValueForKeyPath：ofObject：change：context只是不执行.据我了解,这不取决于streamURL,它是否正确.它必须从AVPlayerItemStatusUnkNown将状态更改为AVPlayerItemStatusReadyToPlay或AVPlayerItemStatusFailed.但是,我在浏览器中检查了该URL,它运行正常.所以有什么问题？我观看了WWDC视频,它说,如果你有音频流,请在AVAsset之前使用AVPLayerItem.

这是我的代码：

- (void) prepare
{
    NSURL * trackStreamURL = [NSURL URLWithString:streamURL];
    NSLog(@"STREAM URL: %@",trackStreamURL);
    _playerItem = [AVPlayerItem playerItemWithURL:trackStreamURL];
    [_playerItem addObserver:self forKeyPath:@"status" options:0 context:nil];
}
- (void) observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"KEY PATH    : %@",keyPath);
    NSLog(@"CHANGE      : %@",changE);
}

提前致谢！

AVPlayer *player = [AVPlayer playerWithPlayerItem:playerItem];