我有一个处理 AVPlayer（和 AVPlayerItem）的类，它向委托报告返回状态、时间和 timedMetadata。
效果很好，除了大约 70-80% 的时间，初始 timedMetadata 不是“观察到的键值”。但是，在错过了第一个 timedMetadata 实例之后，似乎可以毫无问题地观察到所有其他 timedMetadata。
作为一个临时修复，我已经开始在视频的开头嵌入虚拟的 timedMetadata 标签，可以说除了“踢轮胎”之外什么都不做，之后一切正常。然而，这似乎很笨拙。我怀疑要么我以次优方式设置 AVPlayerItem 和 KVO，要么这里只是一个错误。
任何关于为什么会发生这种情况的想法都非常感谢！下面的代码......
// CL: Define constants for the key-value observation contexts.
static const NSString *ItemStatusContext;
static const NSString *ItemMetadataContext;
static const NSString *ItemPlaybackForcastContext;
- (id)initWithURL:(NSURL *)url
{
if (self = [super init]) {
__weak TFPAVController *_self = self;
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:url options:nil];
NSString *tracksKey = @"tracks";
[asset loadValuesAsynchronouslyForKeys:[NSArray arrayWithObject:tracksKey] completionHandler:
^{
dispatch_async(dispatch_get_main_queue(),
^{
NSError *error = nil;
AVKeyValueStatus status = [asset statusOfValueForKey:tracksKey error:&error];
if (status == AVKeyValueStatusLoaded) {
AVPlayerItem *item = [AVPlayerItem playerItemWithAsset:asset];
[item addObserver:_self forKeyPath:@"status" options:0 context:&ItemStatusContext];
[item addObserver:_self forKeyPath:@"timedMetadata" options:0 context:&ItemMetadataContext];
[item addObserver:_self forKeyPath:@"playbackLikelyToKeepUp" options:0 context:&ItemPlaybackForcastContext];
[[NSNotificationCenter defaultCenter] addObserver:_self
selector:@selector(playerItemDidReachEnd:)
name:AVPlayerItemDidPlayToEndTimeNotification
object:item];
AVPlayer *player = [AVPlayer playerWithPlayerItem:item];
_self.totalRunTime = CMTimeGetSeconds(item.duration);
[_self.delegate avPlayerNeedsView:player];
_self.playerItem = item;
_self.player = player;
}
else {
NSLog(@"The asset's tracks were not loaded: %@ // [%@ %@]",
error.localizedDescription,
NSStringFromClass([self class]),
NSStringFromSelector(_cmd));
}
_self.playerObserver = [_self.player addPeriodicTimeObserverForInterval:CMTimeMake(1, _FrameRate_)
queue:NULL
usingBlock: ^(CMTime time) {
_self.currentVideoTime = CMTimeGetSeconds([_self.playerItem currentTime]);
}];
});
}];
}
return self;
}
#pragma mark - KVO Response Methods
- (void)observeValueForKeyPath:(NSString *)keyPath
ofObject:(id)object
change:(NSDictionary *)change
context:(void *)context
{
__weak TFPAVController *_self = self;
if (context == &ItemStatusContext) {
dispatch_async(dispatch_get_main_queue(),
^{
if (((AVPlayerItem *)object).status == AVPlayerItemStatusReadyToPlay) {
[_self.delegate videoIsLoadedInPlayer:_self];
}
});
return;
}
else if (context == &ItemMetadataContext) {
dispatch_async(dispatch_get_main_queue(),
^{
[_self checkMetaDataForPlayerItem: (AVPlayerItem *)object];
});
return;
}
else if (context == &ItemPlaybackForcastContext) {
dispatch_async(dispatch_get_main_queue(),
^{
AVPlayerItem *playerItem = object;
if (CMTimeGetSeconds([playerItem currentTime]) <= 0) return;
NSDictionary *notificationDictionary = [NSDictionary dictionaryWithObject:[NSNumber numberWithBool:playerItem.playbackLikelyToKeepUp]
forKey:kAVPlayerStateKey];
[[NSNotificationCenter defaultCenter] postNotificationName:kAVPlayerNotification
object:self
userInfo:notificationDictionary];
});
return;
}
[super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
}
- (void)checkMetaDataForPlayerItem:(AVPlayerItem *)item
{
NSMutableDictionary *metaDict = [NSMutableDictionary dictionary];
// CL: make sure there's stuff there
if (item.timedMetadata != nil && [item.timedMetadata count] > 0) {
// CL: if there is, cycle through the items and create a Dictionary
for (AVMetadataItem *metadata in item.timedMetadata) {
[metaDict setObject:[metadata valueForKey:@"value"] forKey:[metadata valueForKey:@"key"]];
}
// CL: pass it to the delegate
[self.delegate parseNewMetaData:[NSDictionary dictionaryWithDictionary:metaDict]];
}
}