重播 AVPlayerItem / AVPlayer 无需重新下载

Question

我有一个 AVPlayer class 全部设置为流式传输音频文件。它有点长，所以我不能 post 全部放在这里。我坚持的是如何让用户在听完一次音频文件后重播。当它第一次完成时，我正确地收到了通知 AVPlayerItemDidPlayToEndTimeNotification。当我去重播它时，我立即收到相同的通知，这阻止了我重播它。

我怎样才能重置它，使 AVPlayerItem 不认为它已经播放了音频文件？我可以取消分配所有内容并重新设置，但我相信这会迫使用户再次下载音频文件，这是毫无意义且缓慢的。

以下是 class 中我认为相关的部分内容。我尝试重放文件时得到的输出如下所示。前两行完全符合我的预期，但第三行令人惊讶。

is playing
no timer
audio player has finished playing audio

- (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

您可以在播放器收到 AVPlayerItemDidPlayToEndTimeNotification

时调用 seekToTime 方法

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

Answer 2

Apple 建议使用 AVQueueplayer 和 AVPlayerLooper。

这里是 Apple 的（稍微修改过的）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];

AVPlayerLooper 为您完成所有事件的监听和播放，队列播放器用于创建他们所谓的 "treadmill pattern"。这种模式本质上是在队列播放器中链接相同 AVAssetItem 的多个实例，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（在这种情况下是相同的资产，但它的开始仍然需要预滚动）到达之前预滚动，减少资产结束和循环之间的延迟开始。

这在 ~15:00 的视频中有更详细的描述：https://developer.apple.com/videos/play/wwdc2016/503/

重播 AVPlayerItem / AVPlayer 无需重新下载

Replaying AVPlayerItem / AVPlayer without re-downloading

audio

objective-c

ios

avplayer

avplayeritem