86

我正在尝试播放一个从前一个（存储在变量中）MP3传递给的文件。UIViewUIViewNSURL *fileURL

我正在初始化一个AVPlayer：

player = [AVPlayer playerWithURL:fileURL];

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

我认为的NSLog打印Player created:0,意味着它还没有准备好播放。

当我点击播放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??");
    }

}

当我运行它时，我总是进入Error in player??控制台。但是，如果我用一个简单的 ... 替换if检查是否AVPlayer准备好播放的条件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，我该怎么做才能让播放正常工作UIButton？（即，我如何确保AVPlayer不仅已创建，而且还可以播放？）

4

10 回答 10

130

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（请参阅AV Foundation Programming Guide）

但是在点击播放按钮之前，您似乎没有等待播放器准备好。我要做的是禁用此按钮并仅在播放器准备好时启用它。

使用 KVO，可以通知播放器状态的变化：

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

当状态改变时会调用这个方法：

- (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
        }
    }
}
于 2011-03-23T09:33:19.100 回答
35

迅捷解决方案

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：您必须保留观察者变量，否则它将取消分配并且不再调用 changeHandler。因此，不要将观察者定义为函数变量，而是将其定义为实例变量，就像给定的示例一样。

这种键值观察器语法是 Swift 4 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/内容.swift

于 2017-12-13T07:42:42.330 回答
31

我在试图弄清楚一个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。有时他们AVPlayer告诉我它已经准备好播放（使用AVPlayerStatusReadyToPlay），而实际上似乎并没有。我使用了 Jilouc 的 KVO 方法，但并非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's的loadedTimeRanges属性（它是一个）来查询 AVPlayer 加载的流的数量。AVPlayercurrentItemAVPlayerItem

这有点令人困惑，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
}
于 2012-03-17T03:19:26.857 回答
17 
private var playbackLikelyToKeepUpContext = 0

对于注册观察员

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

聆听观察者

 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
        }
    }
}

移除观察者

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

代码中的关键点是实例属性isPlaybackLikelyToKeepUp。

于 2017-06-16T13:18:42.433 回答
11

经过大量研究并尝试了多种方法后，我注意到通常status观察者并不能更好地知道AVPlayer对象何时准备好播放，因为对象可以准备好播放，但这并不意味着它会立即播放。

知道这一点的更好主意是使用loadedTimeRanges.

注册观察者

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

聆听观察者

- (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
    }
}
于 2016-03-10T20:13:50.117 回答
7

根据Tim Camber 的回答，这里是我使用的 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
    }
}
于 2017-04-27T10:43:48.257 回答
5

我遇到了没有收到任何回调的问题。

原来这取决于你如何创建流。在我的例子中，我使用 playerItem 来初始化，因此我不得不将观察者添加到项目中。

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"];
}
于 2015-08-26T09:10:22.863 回答
5

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!!
        }
}
于 2019-07-03T11:51:25.393 回答
3

检查播放器 currentItem 的状态：

if (player.currentItem.status == AVPlayerItemStatusReadyToPlay)
于 2011-03-23T06:27:46.367 回答
2

@JoshBernfeld 的回答对我不起作用。不知道为什么。他观察到playerItem.observe(\.status。我不得不观察player?.observe(\.currentItem?.status。似乎他们是同一件事，playerItem status财产。

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
    }
}

当您使用完播放器集时playerStatusObserver = nil

于 2020-06-17T06:07:15.123 回答