使用 CAKeyframeAnimation 在视频上添加动画层

Question

我正在尝试向我的视频添加一个叠加层，其中包含一个内容随时间变化的子层。所以我将CAKeyframeAnimation 添加到图层中，如下所示：

CALayer *overlayLayer = [CALayer layer];
[overlayLayer setFrame:CGRectMake(0, 0, size.width, size.height)];
[overlayLayer setMasksToBounds:YES];

NSArray *frames = [self.gifImage frames];

CALayer *aLayer = [CALayer layer];
UIImage *firstImage = [frames objectAtIndex:0];
CGFloat nativeWidth = CGImageGetWidth(firstImage.CGImage);
CGFloat nativeHeight = CGImageGetHeight(firstImage.CGImage);
CGRect frame = CGRectMake(0.0, 0.0, nativeWidth, nativeHeight);
aLayer.frame = frame;
aLayer.contents = (id)firstImage.CGImage;
[aLayer setMasksToBounds:YES];

CAKeyframeAnimation *animationSequence = [CAKeyframeAnimation animationWithKeyPath:@"contents"];
animationSequence.calculationMode = kCAAnimationDiscrete;
animationSequence.duration = [self.gifImage totalDuration];
animationSequence.repeatCount = HUGE_VALF;

NSMutableArray *animationSequenceArray = [[NSMutableArray alloc] init];
for (UIImage *image in frames) {
    [animationSequenceArray addObject:(id)image.CGImage];
}

animationSequence.values = animationSequenceArray;
[aLayer addAnimation:animationSequence forKey:@"contents"];
[overlayLayer addSublayer:aLayer];

CALayer *parentLayer = [CALayer layer];
CALayer *videoLayer = [CALayer layer];
parentLayer.frame = CGRectMake(0, 0, size.width, size.height);
videoLayer.frame = CGRectMake(0, 0, size.width, size.height);
[parentLayer addSublayer:videoLayer];
[parentLayer addSublayer:overlayLayer];

composition.animationTool = [AVVideoCompositionCoreAnimationTool
                             videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];

不知何故，当我将aLayer 添加为视图的子层时，它会正确地进行动画处理。但是当我将它添加到视频的叠加层时，动画不起作用。我在这里缺少什么吗？任何帮助表示赞赏。

Answer 1

如果您使用 kCAAnimationDiscrete，这里有一个清单：

• keyTimes 需要一个 0-1 的值，而不是时间
• keyTimes 必须从 0.0 开始并以值 1.0 结束
• keyTimes 的值必须比动画帧数多一个

Answer 2

我终于设法通过将calculationMode 更改为kCAAnimationLinear 来解决此问题。这似乎是一个愚蠢的问题，但我希望它可能对某人有用。