了解 AVPlayer 对象何时准备好播放

Question

我正在尝试播放从先前的 UIView 传递到 UIView 的 MP3 文件（存储在 NSURL *fileURL 中） 变量）。

我正在初始化一个 AVPlayer ：

player = [AVPlayer playerWithURL:fileURL];

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

NSLog 打印 Playercreated:0, 我认为这意味着它还没有准备好播放。

当我单击播放UIButton时，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??");
    }

}

当我运行此代码时，我总是在控制台中收到播放器错误？。 但是，如果我用简单的 if(!isPlaying)... 替换检查 AVPlayer 是否准备好播放的 if 条件，那么我第二次点击播放 UIButton 时，音乐开始播放。

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**

我第二次看到，player.status 似乎保持为 1，我猜测是 AVPlayerReadyToPlay。

我该怎么做才能让播放在我第一次单击播放 UIButton 时正常工作？ （即，我如何确保 AVPlayer 不仅已创建，而且已准备好播放？）

Answer 1

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

但是您似乎没有等到播放器准备好后再点击播放按钮。我想要的是禁用此按钮并仅在播放器准备好时才启用它。

使用KVO，可以收到玩家状态变化的通知：

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

当状态变化时将调用此方法：

- (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

Swift 解决方案

var observer: NSKeyValueObservation?

func prepareToPlay() {
    let url = <#Asset URL#>
    // Create asset to be played.
    let asset = AVAsset(url: url)
    
    // Create a new AVPlayerItem with the asset.
    let playerItem = AVPlayerItem(asset: asset)
    
    // 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：您必须保留观察者变量，否则它将释放并且将不再调用changeHandler。因此，不要将观察者定义为函数变量，而是将其定义为实例变量，如给定的示例。

此键值观察器语法是 Swift 4 中的新语法。

有关更多信息，请参阅此处 https://github.com/ole/whats-new-in-swift-4/blob/master/Whats-new-in-Swift-4.playground/Pages/Key%20paths.xcplaygroundpage/Contents.swift

Answer 3

我在尝试找出 AVPlayer 的状态时遇到了很多麻烦。 status 属性似乎并不总是很有帮助，当我尝试处理音频会话中断时，这导致了无尽的挫败感。有时，AVPlayer 告诉我它已准备好播放（使用 AVPlayerStatusReadyToPlay），但实际上似乎并未准备好。我使用了 Jilouc 的 KVO 方法，但它并不是在所有情况下都有效。

作为补充，当 status 属性没有用时，我通过查看 AVPlayer 的 loadedTimeRanges 属性来查询 AVPlayer 已加载的流量。 currentItem（这是一个 AVPlayerItem）。

这一切都有点令人困惑，但它看起来是这样的：

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 4

private var playbackLikelyToKeepUpContext = 0

对于注册观察者

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

监听观察者

 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
        }
    }
}

对于删除观察者

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

代码中的关键点是实例属性 isPlaybackLikelyToKeepUp。

Answer 5

经过大量研究并尝试多种方法后，我注意到通常 status 观察者并不能更好地了解 AVPlayer 对象何时准备好播放，因为该对象可以准备播放，但这并不意味着它将立即播放。

了解这一点的更好方法是使用 loadedTimeRanges。

对于注册观察者

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

倾听观察者的声音

- (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 或在注册观察者之前），它是调用的好地方

- (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 6

基于 Tim Camber 回答，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

我遇到了没有收到任何回调的问题。

事实证明，这取决于您创建流的方式。在我的例子中，我使用了一个playerItem来初始化，因此我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!!
        }
}

Answer 9

@JoshBernfeld 的答案对我不起作用。不知道为什么。他观察了playerItem.observe(\.status)。我必须观察player?.observe(\.currentItem?.status。看起来它们是同一件事， playerItem status 属性设置playerStatusObserver = nil

var playerStatusObserver: NSKeyValueObservation?

player?.automaticallyWaitsToMinimizeStalling = false // starts faster

playerStatusObserver = player?.observe(\.currentItem?.status, options: [.new, .old]) { (player, change) in
        
    switch (player.status) {
    case .readyToPlay:
            // here is where it's ready to play so play player
            DispatchQueue.main.async { [weak self] in
                self?.player?.play()
            }
    case .failed, .unknown:
            print("Media Failed to Play")
    @unknown default:
         break
    }
}

当您使用完播放器后，

Answer 10

检查玩家当前物品的状态：

if (player.currentItem.status == AVPlayerItemStatusReadyToPlay)