AVPlayer项目缓冲区为空

Question

我使用播放流内容的AVPlayer。我想知道缓冲区为空的时间和准备好播放的时间。但是观察者"playbackBufferEmpty"one_answers"playbackLikelyToKeepUp"并不是每次都按需要工作。他们有时工作，但经常不工作。我只在OSX 10.7.5下使用iPad模拟器iOS 6.1。以下是我如何设置和监听观察员：

- (void)playAudioStream:(NSURL *)audioStreamURL
{
 if(_audioPlayer && _audioPlayer.currentItem)
 {
     [_audioPlayer removeObserver:self forKeyPath:StatusKey];
     [_audioPlayer.currentItem removeObserver:self forKeyPath:@"playbackBufferEmpty"];
     [_audioPlayer.currentItem removeObserver:self forKeyPath:@"playbackLikelyToKeepUp"];
 }
 AVPlayerItem *playerItem = [AVPlayerItem playerItemWithURL:audioStreamURL];
 [playerItem addObserver:self forKeyPath:@"playbackBufferEmpty" options:NSKeyValueObservingOptionNew context:nil];
 [playerItem addObserver:self forKeyPath:@"playbackLikelyToKeepUp" options:NSKeyValueObservingOptionNew context:nil];
 _audioPlayer = [AVPlayer playerWithPlayerItem:playerItem];
 [_audioPlayer addObserver:self forKeyPath:StatusKey options:NSKeyValueObservingOptionNew context:nil];
 //[_audioPlayer replaceCurrentItemWithPlayerItem:playerItem];
 //_audioPlayer.actionAtItemEnd = AVPlayerActionAtItemEndNone;
 [_audioPlayer play];
}
...
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
 if ([keyPath isEqualToString:@"playbackBufferEmpty"] )
 {
    if (_audioPlayer.currentItem.playbackBufferEmpty)
    {
       ...
    }
 }
 if ([keyPath isEqualToString:@"playbackLikelyToKeepUp"])
 {
    if (_audioPlayer.currentItem.playbackLikelyToKeepUp)
    {
        ...
    }
 }
}

请帮助我获得"缓冲区为空"one_answers"缓冲区准备就绪"事件的正确方法（例如，当Internet连接断开时）。非常感谢。

Answer 1

添加观察者时需要使用上下文。这是您的示例代码。

初始化上下文

static void *playbackLikelyToKeepUpKVOToken = &playbackLikelyToKeepUpKVOToken;
static void *playbackBufferEmpty = &playbackBufferEmpty;
static void *playbackBufferFull = &playbackBufferFull;

添加观察员

[self.playerItem removeObserver:self forKeyPath:@"playbackBufferEmpty" context:playbackBufferEmpty];
[self.playerItem removeObserver:self forKeyPath:@"playbackLikelyToKeepUp" context:playbackLikelyToKeepUpKVOToken];
[self.playerItem removeObserver:self forKeyPath:@"playbackBufferFull" context:playbackBufferFull];

处理

if (context == playbackLikelyToKeepUpKVOToken)
{
    if (self.playerItem.playbackLikelyToKeepUp)
    {
        NSLog(@"recieve playbackLikelyToKeepUp");
    }
}
else if (context == playbackBufferEmpty)
{
    if (self.playerItem.playbackBufferEmpty)
    {
        NSLog(@"recieve playbackBufferEmpty");
    }
}
else if(context == playbackBufferFull)
{
    NSLog(@"recieve playbackBufferFull");
}
else
{
    [super observeValueForKeyPath:path ofObject:object change:change context:context];
}

Answer 2

@Nghia Tran的回答帮助了我。他只是混淆了添加观察员/删除观察员（我们需要两者）

添加观察员：

[self.playerItem addObserver:self forKeyPath:@"playbackBufferEmpty" options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew  context:playbackBufferEmpty];
[self.playerItem addObserver:self forKeyPath:@"playbackLikelyToKeepUp" options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew  context:playbackLikelyToKeepUpKVOToken];
[self.playerItem addObserver:self forKeyPath:@"playbackBufferFull" options:NSKeyValueObservingOptionInitial | NSKeyValueObservingOptionNew   context:playbackBufferFull];

删除观察员：

[self.playerItem removeObserver:self forKeyPath:@"playbackBufferEmpty" context:playbackBufferEmpty];
[self.playerItem removeObserver:self forKeyPath:@"playbackLikelyToKeepUp" context:playbackLikelyToKeepUpKVOToken];
[self.playerItem removeObserver:self forKeyPath:@"playbackBufferFull" context:playbackBufferFull];