AVPlayer replaceCurrentItemWithPlayerItem 打破 UIViewAnimation

Posted 2023-03-13

【中文标题】AVPlayer replaceCurrentItemWithPlayerItem 打破 UIViewAnimation

【英文标题】：AVPlayer replaceCurrentItemWithPlayerItem breaking UIViewAnimation

【发布时间】：2012-07-31 16:07:04

【问题描述】：

我有两个交叉淡入淡出的视图控制器，它们都在它们的子视图中播放视频。视图 A 中的视频在淡入开始时开始播放，在淡出结束时停止。视图 B 中的视频从淡入开始，在淡出后停止。基本的东西。 我让它与 MPMoviePlayerController 一起正常工作，但我也想做音频淡入/淡出，这迫使我使用 AVFoundationFramework 中的 AVPlayer。基本上一切似乎都很好，但我注意到开关导致淡入中断。视图 B alpha 只是从 0 跳到 1，并且 UIView animateWithDuration 的完成块被调用为 false 值。 我注意到只有在 loadView 方法期间我在 AVPlayer 对象上调用 replaceCurrentItemWithPlayerItem: 方法时才会发生这种情况。

淡入淡出的代码如下所示：

- (void)pushViewController:(UIViewController *)viewController duration:(float)duration
    
    float halfFadeInOutTime = duration/2.0;
    viewController.view.alpha = 0.0;
    UIView *tmpView = self.view;


    [viewController viewWillAppear:YES];

    //start fading out the first view
    [UIView animateWithDuration:halfFadeInOutTime 
                          delay:0 
                        options:UIViewAnimationOptionBeginFromCurrentState | UIViewAnimationOptionAllowUserInteraction
                     animations:^
                         tmpView.alpha = 0.0;
                      
                     completion:^(BOOL finished)
                         if( finished )
                             if( [self respondsToSelector:@selector(fadeOutFinished:)] )
                                 [self fadeOutFinished:duration];
                             


                             [self.navigationController pushViewController:viewController animated:NO];

                             //start fading in with the second view
                             [UIView animateWithDuration:halfFadeInOutTime 
                                                   delay:0
                                                 options:UIViewAnimationOptionBeginFromCurrentState | UIViewAnimationOptionAllowUserInteraction
                                              animations:^
                                                  viewController.view.alpha = 1.0;
                                               
                                              completion:^(BOOL finished2)
                                                  if( finished2 )
                                                      if( [((CrossfadeableViewController*)viewController) respondsToSelector:@selector(fadeInFinished:)] )
                                                          [((CrossfadeableViewController*)viewController) fadeInFinished:duration];
                                                      
                                                  
                                              
                              ];

                             if( [((CrossfadeableViewController*)viewController) respondsToSelector:@selector(fadeInStarted:)] )
                                 [((CrossfadeableViewController*)viewController) fadeInStarted:duration];
                             


                         
                     
     ];

    if( [self respondsToSelector:@selector(fadeOutStarted:)] )
        [self fadeOutStarted:duration];
    

loadView中的AVPlayer相关代码是这样的

- (void) loadView

    [super loadView]

    //...

    /* 
     * Variables of type:
     * UIView *videoPlaceholder;
     * AVURLAsset *asset;
     * AVPlayerItem *playerItem;
     * AVPlayer *player;
     * AVPlayerLayer *playerLayer;
     */ 

    videoPlaceholder = [[UIView alloc] initWithFrame:_frame];

    playerLayer = [[AVPlayerLayer alloc] init];
    [playerLayer setFrame:videoPlaceholder.frame];
    playerLayer.videoGravity = AVLayerVideoGravityResizeAspect;
    player = [[AVPlayer alloc] init];

    NSString *_url = [[NSBundle mainBundle] pathForResource:[_videoFilename stringByDeletingPathExtension] ofType:[_videoFilename pathExtension]];
    if( _url != nil )
        NSURL *url = [NSURL fileURLWithPath:_url];

        asset = [AVURLAsset URLAssetWithURL:url options:nil];

        playerItem = [AVPlayerItem playerItemWithAsset:asset];

        [player replaceCurrentItemWithPlayerItem:playerItem];
        [player seekToTime:kCMTimeZero];
        [player setActionAtItemEnd:AVPlayerActionAtItemEndNone];
    



    playerLayer.player = player;
    [videoPlaceholder.layer addSublayer:playerLayer];

    [self.view addSubview:videoPlaceholder];

    //....

有谁知道什么会导致动画中断？由于在交叉淡入淡出开始之前调用了 loadView ，因此在动画期间我没有更改视图中的任何内容。什么会导致相同的代码与 MPMoviePlayerController 一起工作并与 AVPlayer 中断？

干杯， 铅

【参考方案1】：

事实证明这是加载 AVPlayerItem 的问题。我必须等到电影加载完毕 - 否则动画淡入就会中断

等待视频加载完毕的示例代码：

- (void)observeValueForKeyPath:(NSString*) path 
                  ofObject:(id)object 
                    change:(NSDictionary*)change 
                   context:(void*)context 
  if (context == AVPlayerDemoPlaybackViewControllerStatusObservationContext) 
      AVPlayerStatus status = [[change objectForKey:NSKeyValueChangeNewKey] integerValue];
      if (status == AVPlayerStatusReadyToPlay) 
        if( [self.videoStateChangeDelegate respondsToSelector:@selector(videoStateChangedToReadyForPlayback)] )
            [self.videoStateChangeDelegate videoStateChangedToReadyForPlayback];
        
        [self.player play];
      
  

[self.videoStateChangeDelegate videoStateChangedToReadyForPlayback] 通知我的委托控制器它可以开始淡入。 太糟糕了，因为这个问题，我的简单代码变得有点复杂。