知道AVPlayer对象何时可以播放

Question

我正在尝试播放一个MP3传递给UIView前一个文件的文件UIView(存储在一个NSURL *fileURL变量中).

我正在初始化一个AVPlayer:

player = [AVPlayer playerWithURL:fileURL];

NSLog(@"Player created:%d",player.status);

我想的NSLog印刷品Player created:0,意味着它尚未准备好播放.

当我点击播放时UIButton,我运行的代码是:

-(IBAction)playButtonClicked
{
    NSLog(@"Clicked Play. MP3:%@",[fileURL absoluteString]);

    if(([player status] == AVPlayerStatusReadyToPlay) && !isPlaying)
//  if(!isPlaying)
    {
        [player play];
        NSLog(@"Playing:%@ with %d",[fileURL absoluteString], player.status);
        isPlaying = YES;
    }
    else if(isPlaying)
    {

        [player pause];
        NSLog(@"Pausing:%@",[fileURL absoluteString]);
        isPlaying = NO;
    }
    else {
        NSLog(@"Error in player??");
    }

}

当我运行它时,我总是进入Error in player??控制台.然而,如果我用一个简单的...... 替换if检查是否AVPlayer准备播放的条件if(!isPlaying),那么音乐将播放第二次我点击播放UIButton.

控制台日志是:

Clicked Play. MP3:http://www.nimh.nih.gov/audio/neurogenesis.mp3
Playing:http://www.nimh.nih.gov/audio/neurogenesis.mp3 **with 0**

Clicked Play. MP3:http://www.nimh.nih.gov/audio/neurogenesis.mp3
Pausing:http://www.nimh.nih.gov/audio/neurogenesis.mp3

Clicked Play. MP3:http://www.nimh.nih.gov/audio/neurogenesis.mp3
2011-03-23 11:06:43.674 Podcasts[2050:207] Playing:http://www.nimh.nih.gov/audio/neurogenesis.mp3 **with 1**

我看到第二次,player.status似乎持有1,我猜是AVPlayerReadyToPlay.

第一次点击播放时,我该怎么做才能使播放正常工作UIButton？(也就是说,我怎样才能确保AVPlayer不仅仅是创造了,还准备好了？)

Answer 1

您正在播放远程文件.AVPlayer缓冲足够的数据并准备好播放文件可能需要一些时间(参见AV Foundation编程指南)

但是,在点击播放按钮之前,您似乎还没等待播放器准备就绪.我想要的是禁用此按钮并仅在播放器准备就绪时启用它.

使用KVO,可以通知玩家状态的变化:

playButton.enabled = NO;
player = [AVPlayer playerWithURL:fileURL];
[player addObserver:self forKeyPath:@"status" options:0 context:nil];   

状态更改时将调用此方法:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
                        change:(NSDictionary *)change context:(void *)context {
    if (object == player && [keyPath isEqualToString:@"status"]) {
        if (player.status == AVPlayerStatusReadyToPlay) {
            playButton.enabled = YES;
        } else if (player.status == AVPlayerStatusFailed) {
            // something went wrong. player.error should contain some information
        }
    }
}

Answer 2

我在试图弄清楚状态时遇到了很多麻烦AVPlayer.该status属性似乎并不总是非常有用,当我试图处理音频会话中断时,这导致了无尽的挫败感.有时AVPlayer告诉我它准备播放(有AVPlayerStatusReadyToPlay)它实际上似乎没有.我使用了Jilouc的KVO方法,但它并不适用于所有情况.

为了补充,当status属性没有用时,我通过查看's 的loadedTimeRanges属性(这是一个)来查询AVPlayer加载的流的数量.AVPlayercurrentItemAVPlayerItem

这有点令人困惑,但这就是它的样子:

NSValue *val = [[[audioPlayer currentItem] loadedTimeRanges] objectAtIndex:0];
CMTimeRange timeRange;
[val getValue:&timeRange];
CMTime duration = timeRange.duration;
float timeLoaded = (float) duration.value / (float) duration.timescale; 

if (0 == timeLoaded) {
    // AVPlayer not actually ready to play
} else {
    // AVPlayer is ready to play
}

Answer 3

快速解决方案

var observer: NSKeyValueObservation?

func prepareToPlay() {
    let url = <#Asset URL#>
    // Create asset to be played
    let asset = AVAsset(url: url)

    let assetKeys = [
        "playable",
        "hasProtectedContent"
    ]
    // Create a new AVPlayerItem with the asset and an
    // array of asset keys to be automatically loaded
    let playerItem = AVPlayerItem(asset: asset,
                              automaticallyLoadedAssetKeys: assetKeys)

    // Register as an observer of the player item's status property
    self.observer = playerItem.observe(\.status, options:  [.new, .old], changeHandler: { (playerItem, change) in
        if playerItem.status == .readyToPlay {
            //Do your work here
        }
    })

    // Associate the player item with the player
    player = AVPlayer(playerItem: playerItem)
}

您也可以通过这种方式使观察者无效

self.observer.invalidate()

重要提示:必须保留observer变量,否则它将解除分配并且不再调用changeHandler.因此,不要将观察者定义为函数变量,而是将其定义为类似给定示例的实例变量.

这个键值观察器语法是Swift 4的新功能.

有关详细信息,请参阅https://github.com/ole/whats-new-in-swift-4/blob/master/Whats-new-in-Swift-4.playground/Pages/Key%20paths.xcplaygroundpage/ Contents.swift

Answer 4

在研究了很多并尝试了许多方法后,我注意到通常情况下status观察者在AVPlayer对象准备好玩的时候并不是更好,因为对象可以准备好玩,但这并不意味着它会立即发挥.

了解这一点的好主意是loadedTimeRanges.

对于注册观察员

[playerClip addObserver:self forKeyPath:@"currentItem.loadedTimeRanges" options:NSKeyValueObservingOptionNew context:nil];

听观察者说

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{
    if (object == playerClip && [keyPath isEqualToString:@"currentItem.loadedTimeRanges"]) {
        NSArray *timeRanges = (NSArray*)[change objectForKey:NSKeyValueChangeNewKey];
        if (timeRanges && [timeRanges count]) {
            CMTimeRange timerange=[[timeRanges objectAtIndex:0]CMTimeRangeValue];
            float currentBufferDuration = CMTimeGetSeconds(CMTimeAdd(timerange.start, timerange.duration));
            CMTime duration = playerClip.currentItem.asset.duration;
            float seconds = CMTimeGetSeconds(duration);

            //I think that 2 seconds is enough to know if you're ready or not
            if (currentBufferDuration > 2 || currentBufferDuration == seconds) {
                // Ready to play. Your logic here
            }
        } else {
            [[[UIAlertView alloc] initWithTitle:@"Alert!" message:@"Error trying to play the clip. Please try again" delegate:nil cancelButtonTitle:@"Ok" otherButtonTitles:nil, nil] show];
        }
    }
}

对于删除观察者(dealloc,viewWillDissapear或寄存器观察者之前),它是一个被调用的好地方

- (void)removeObserverForTimesRanges
{
    @try {
        [playerClip removeObserver:self forKeyPath:@"currentItem.loadedTimeRanges"];
    } @catch(id anException){
        NSLog(@"excepcion remove observer == %@. Remove previously or never added observer.",anException);
        //do nothing, obviously it wasn't attached because an exception was thrown
    }
}

Answer 5

private var playbackLikelyToKeepUpContext = 0

对于登记观察员

avPlayer.addObserver(self, forKeyPath: "currentItem.playbackLikelyToKeepUp",
        options: .new, context: &playbackLikelyToKeepUpContext)

听观察者说

 override func observeValue(forKeyPath keyPath: String?, of object: Any?, change: [NSKeyValueChangeKey : Any]?, context: UnsafeMutableRawPointer?) {
    if context == &playbackLikelyToKeepUpContext {
        if avPlayer.currentItem!.isPlaybackLikelyToKeepUp {
           // loadingIndicatorView.stopAnimating() or something else
        } else {
           // loadingIndicatorView.startAnimating() or something else
        }
    }
}

删除观察者

deinit {
    avPlayer.removeObserver(self, forKeyPath: "currentItem.playbackLikelyToKeepUp")
}

代码中的关键点是实例属性isPlaybackLikelyToKeepUp.

Answer 6

基于Tim Camber的答案，这是我使用的Swift函数：

private func isPlayerReady(_ player:AVPlayer?) -> Bool {

    guard let player = player else { return false }

    let ready = player.status == .readyToPlay

    let timeRange = player.currentItem?.loadedTimeRanges.first as? CMTimeRange
    guard let duration = timeRange?.duration else { return false } // Fail when loadedTimeRanges is empty
    let timeLoaded = Int(duration.value) / Int(duration.timescale) // value/timescale = seconds
    let loaded = timeLoaded > 0

    return ready && loaded
}

或者，作为扩展

extension AVPlayer {
    var ready:Bool {
        let timeRange = currentItem?.loadedTimeRanges.first as? CMTimeRange
        guard let duration = timeRange?.duration else { return false }
        let timeLoaded = Int(duration.value) / Int(duration.timescale) // value/timescale = seconds
        let loaded = timeLoaded > 0

        return status == .readyToPlay && loaded
    }
}

Answer 7

我没有收到任何回调的问题。

事实证明，这取决于您如何创建流。在我的情况下，我使用playerItem进行初始化，因此必须将观察者添加到该项目中。

例如：

- (void) setup
{
    ...
    self.playerItem = [AVPlayerItem playerItemWithAsset:asset];
    self.player = [AVPlayer playerWithPlayerItem:self.playerItem];
    ... 

     // add callback
     [self.player.currentItem addObserver:self forKeyPath:@"status" options:0 context:nil];
}

// the callback method
- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object
                    change:(NSDictionary *)change context:(void *)context
{
    NSLog(@"[VideoView] player status: %i", self.player.status);

    if (object == self.player.currentItem && [keyPath isEqualToString:@"status"])
    {
        if (self.player.currentItem.status == AVPlayerStatusReadyToPlay)
        {
           //do stuff
        }
    }
}

// cleanup or it will crash
-(void)dealloc
{
    [self.player.currentItem removeObserver:self forKeyPath:@"status"];
}

Answer 8

斯威夫特4：

var player:AVPlayer!

override func viewDidLoad() {
        super.viewDidLoad()
        NotificationCenter.default.addObserver(self, 
               selector: #selector(playerItemDidReadyToPlay(notification:)),
               name: .AVPlayerItemNewAccessLogEntry, 
               object: player?.currentItem)
}

@objc func playerItemDidReadyToPlay(notification: Notification) {
        if let _ = notification.object as? AVPlayerItem {
            // player is ready to play now!!
        }
}