无需重新下载即可重播AVPlayerItem/AVPlayer

Question

我有一个AVPlayer类,所有设置都流式传输音频文件.它有点长,所以我不能在这里发布整个事情.我所坚持的是如何允许用户在完成一次听完之后重放音频文件.当它第一次完成时,我正确收到通知AVPlayerItemDidPlayToEndTimeNotification.当我重播它时,我立即收到相同的通知,阻止我重播它.

我怎么能重置这个,以至于AVPlayerItem不认为它已经播放了音频文件？我可以释放所有内容并重新设置它,但我相信这将迫使用户再次下载音频文件,这是毫无意义和缓慢的.

以下是我认为相关的课程的一些部分.尝试重播文件时得到的输出如下所示.前两行正是我所期望的,但第三行是一个惊喜.

正在播放
没有定时器的
音频播放器已播放音频

- (id) initWithURL : (NSString *) urlString
{
    self = [super init];
    if (self) {
        self.isPlaying = NO;
        self.verbose = YES;

        if (self.verbose) NSLog(@"url: %@", urlString);
        NSURL *url = [NSURL URLWithString:urlString];

        self.playerItem = [AVPlayerItem playerItemWithURL:url];
        self.player = [[AVPlayer alloc] initWithPlayerItem:self.playerItem];

        [self determineAudioPlayTime : self.playerItem];

        self.lengthOfAudioInSeconds = @0.0f;

        [self.player addObserver:self forKeyPath:@"status" options:0 context:nil];

        [[NSNotificationCenter defaultCenter] addObserver:self selector:@selector(itemDidFinishPlaying:) name:AVPlayerItemDidPlayToEndTimeNotification object:self.playerItem];
    }

    return self;
}

// this is what gets called when the user clicks the play button after they have 
// listened to the file and the AVPlayerItemDidPlayToEndTimeNotification has been received
- (void) playAgain {
    [self.playerItem seekToTime:kCMTimeZero];
    [self toggleState];
}

- (void) toggleState {
    self.isPlaying = !self.isPlaying;

    if (self.isPlaying) {
        if (self.verbose) NSLog(@"is playing");
        [self.player play];

        if (!timer) {
            NSLog(@"no timer");
            CMTime audioTimer = CMTimeMake(0, 1);
            [self.player seekToTime:audioTimer];

            timer = [NSTimer scheduledTimerWithTimeInterval:1.0
                                                     target:self
                                                   selector:@selector(updateProgress)
                                                   userInfo:nil
                                                    repeats:YES];
        }

    } else {
        if (self.verbose) NSLog(@"paused");
        [self.player pause];
    }
}

-(void)itemDidFinishPlaying:(NSNotification *) notification {
    if (self.verbose) NSLog(@"audio player has finished playing audio");
    [[NSNotificationCenter defaultCenter] postNotificationName:@"audioFinished" object:self];
    [timer invalidate];
    timer = nil;
    self.totalSecondsPlayed = [NSNumber numberWithInt:0];
    self.isPlaying = NO;
}

Answer 1

当玩家收到AVPlayerItemDidPlayToEndTimeNotification时,您可以调用seekToTime方法

func itemDidFinishPlaying() {
    self.player.seek(to: CMTime.zero)
    self.player.play()
}

Answer 2

Apple 建议AVQueueplayer与AVPlayerLooper.

这是苹果的（稍作修改的）示例代码：

AVQueuePlayer *queuePlayer = [[AVQueuePlayer alloc] init];    

AVAsset *asset = // AVAsset with its 'duration' property value loaded
AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:asset];

 // Create a new player looper with the queue player and template item
self.playerLooper = [AVPlayerLooper playerLooperWithPlayer:queuePlayer
                                              templateItem:playerItem];

 // Begin looping playback
[queuePlayer play];

它AVPlayerLooper会为您监听和播放所有事件，并且队列播放器用于创建他们所谓的“跑步机模式”。此模式本质上是在队列播放器中链接相同的多个实例AVAssetItem，并将每个完成的资产移回队列的开头。

这种方法的优点是，它使框架能够在下一个资产（在本例中是相同的资产，但其开始仍然需要预滚动）到达之前对其进行预滚动，从而减少资产结束和循环开始之间的延迟。

视频中约 15:00 对此进行了更详细的描述：https://developer.apple.com/videos/play/wwdc2016/503/