AVPlayer replaceCurrentItemWithPlayerItem无法在iOS 4.3.3+上运行

Question

我有一个使用AVPlayer构建的音频播放器.

目前,我把player情况和周围时,我需要换轨(无论是从手动选择或轨道已经到达末端),我创建了一个新的AVPlayerItem,我称之为replaceCurrentItemWithPlayerItem新项目.

根据文档,replaceCurrentItemWithPlayerItem是一个异步操作,所以我也观察了播放器的currentItem键路径.当它被调用时,我告诉我的玩家玩.

这是相关代码:

AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:asset];
[playerItem addObserver:self forKeyPath:@"status" options:NSKeyValueObservingOptionNew context:CHStreamingAudioPlayer_PlayerItemStatusChangedContext];

if (!_player) {
    _player = [[AVPlayer alloc] initWithPlayerItem:playerItem]; 
    [_player addObserver:self forKeyPath:@"status"          options:NSKeyValueObservingOptionNew context:CHStreamingAudioPlayer_PlayerStatusChangedContext];
    [_player addObserver:self forKeyPath:@"currentItem"     options:NSKeyValueObservingOptionNew context:CHStreamingAudioPlayer_PlayerCurrentItemChangedContext];
} else {
    [_player replaceCurrentItemWithPlayerItem:playerItem];
}

这里是关键值观察回调:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context {
    if (context == CHStreamingAudioPlayer_PlayerCurrentItemChangedContext) {
        NSLog(@"Player's current item changed! Change dictionary: %@", change);
        if (_player.currentItem) {
            [self play]; //<---- doesn't get called
        }
    } else {
        [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
    }
}

在iOS 4.3.3(和iOS 5)上,我的关键观察方法被调用,但_player.currentItem总是如此nil.在4.2.1和4.3.2上,此属性包含实际值.永远不会再调用此方法.所以从本质上讲,替换似乎总是失败.

这似乎是一个错误,但也许我做错了什么.

Answer 1

我在iOS 5(包括5.0.1)中遇到了这个问题.它曾经在iOS 4.x上正常工作.

有两种方法可以解决此问题,每次需要交换曲目时,都可以AVPlayer使用所需的AVPlayerItems来释放和重新创建.或者,只需调用replaceCurrentItemWithPlayerItem:主线程即可.

我尝试了两种选择,但它们运行良好.

致记自:Apple开发者论坛