ios - 设置 AVSynchonizedLayer

Question

我一直在尝试制作一个将视频与动画对象连接起来的概念证明(本质上，我是在将用户选择的位图“rotoscoping”到特定位置的固定视频上)。在查看了有关 Core Animation(WWDC10 等)和 AVSync..Layer(Apple WWDC10 示例代码、doc 示例代码)的所有可用 Apple 资料后，根本没有足够清晰的独立代码示例来推导如何实现它播放模式正确。

使用 CA，我有一个加载到 CALayer 中的视频资源，以及一个附加到位图的动画，然后连接到另一个 CALayer。我创建了一个 AVSynchronizedLayer 并将两个对象添加为子层。

当这棵树被添加到 UIView 的图层属性时，我期待动画的播放与视频同步运行。相反，我只看到视频在播放，而动画从不执行 - 这里是我的代码的相关部分，它们都位于单个 View Controller 中(在 ViewDidLoad 中调用)。

Video101.m4v = 简单的 m4v 视频， gerald.png = 位图

NSURL *fileURL = [[NSBundle mainBundle] URLForResource:@"Video101" withExtension:@"m4v"];
AVURLAsset *asset = [AVURLAsset URLAssetWithURL:fileURL options:nil];
AVPlayerItem *playerItem = [AVPlayerItem playerItemWithAsset:asset];

AVPlayer *player = [[AVPlayer playerWithPlayerItem:playerItem]retain];
AVPlayerLayer *playerLayer = [AVPlayerLayer playerLayerWithPlayer:player];
playerLayer.frame = CGRectMake(0, 0, 1024, 768);
playerLayer.videoGravity = AVLayerVideoGravityResizeAspectFill;

CALayer *gerald = [CALayer layer];
gerald.frame = CGRectMake(0, 0, 120, 120);
gerald.contents = (id) [UIImage imageNamed:@"gerald.png"].CGImage;

[self.view.layer addSublayer:playerLayer];
[self.view.layer insertSublayer:gerald above:playerLayer];


CAKeyframeAnimation *anim = [CAKeyframeAnimation animationWithKeyPath:@"position"];
anim.duration = 18.0;

anim.values = [NSArray arrayWithObjects:
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(310.0, 400.0)],
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(310.0, 400.0)],
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(310.0, 400.0)],
               [NSValue valueWithCGPoint:CGPointMake(480.0, 206.0)],
               [NSValue valueWithCGPoint:CGPointMake(310.0, 400.0)],
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(310.0, 400.0)],
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(10.0, 760.0)],
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(310.0, 400.0)],
               [NSValue valueWithCGPoint:CGPointMake(320.0, 406.0)],
               [NSValue valueWithCGPoint:CGPointMake(310.0, 400.0)], nil];


anim.keyTimes = [NSArray arrayWithObjects:
                 [NSNumber numberWithFloat:0.02],
                 [NSNumber numberWithFloat:0.06],
                 [NSNumber numberWithFloat:0.09],
                 [NSNumber numberWithFloat:0.1], 
                 [NSNumber numberWithFloat:0.12],
                 [NSNumber numberWithFloat:0.2],
                 [NSNumber numberWithFloat:0.25],
                 [NSNumber numberWithFloat:0.32], 
                 [NSNumber numberWithFloat:0.38],
                 [NSNumber numberWithFloat:0.49],
                 [NSNumber numberWithFloat:0.53],
                 [NSNumber numberWithFloat:0.59], 
                 [NSNumber numberWithFloat:0.63],
                 [NSNumber numberWithFloat:0.69],
                 [NSNumber numberWithFloat:0.78],
                 [NSNumber numberWithFloat:0.81], 
                 [NSNumber numberWithFloat:0.91], 
                 [NSNumber numberWithFloat:1.0], nil];


AVSynchronizedLayer *syncLayer = [AVSynchronizedLayer synchronizedLayerWithPlayerItem:playerItem];
[syncLayer addSublayer:gerald];
[gerald addAnimation:anim forKey:@"transform.position"];

[self.view.layer addSublayer:syncLayer];

[player play];

实现 AVSynchronizedLayer 的正确格式或方式是什么，以便动画和视频一起播放？

Answer 1

除了一位之外，您的 CAKeyframeAnimation 设置正确: 根据 WWDC“使用 AV Foundation 编辑媒体”讲座，您需要将动画的 beginTime 属性设置为非零值。

Zero beginTime is automatically translated to CACurrentMediaTime(). Use a small nonzero number: e.g., 1e-100 or -1e-100 (AVCoreAnimationBeginTimeAtZero)

我认为如果您添加 anim.beginTime = AVCoreAnimationBeginTimeAtZero;，您会发现动画会在视频开始播放时立即开始。