CALayer动画问题

Question

我正在尝试动画不同的CALayers，但只有最后一个动画作品。

我这样做是为了创建包含文本的不同CALayers，并为每一个都添加动画。下面是生成CALayers的代码：

    // Create a layer for the title
    CALayer *_watermarkLayer = [CALayer layer];
    [_watermarkLayer setOpacity:0];

    // Create a layer for the text of the title.
    CATextLayer *titleLayer = [CATextLayer layer];
    titleLayer.string = text;
    titleLayer.foregroundColor = [color CGColor];
    titleLayer.shadowOpacity = 0.5;
    titleLayer.alignmentMode = kCAAlignmentCenter;
    titleLayer.bounds = CGRectMake(0, 0, videoSize.width/2, videoSize.height/2); 
    [_watermarkLayer addSublayer:titleLayer];

    // Fade in/out animation
    NSString* aux = [NSString stringWithFormat:@"%d", seconds];
    CABasicAnimation *fadeAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
    fadeAnimation.fromValue = [NSNumber numberWithFloat:1.0];
    fadeAnimation.toValue = [NSNumber numberWithFloat:0.0];
    fadeAnimation.additive = YES;
    fadeAnimation.removedOnCompletion = YES;
    fadeAnimation.beginTime = seconds;
    fadeAnimation.duration = 2.0;
    fadeAnimation.fillMode = kCAFillModeRemoved; 
    [_watermarkLayer addAnimation:fadeAnimation forKey:[@"animateOpacity" stringByAppendingString:aux]];

我使用从上面的代码中获得的CALayer，如下所示：

- (void) addWatermarkWithVideoComposition:(AVMutableVideoComposition*)videoComposition withLabel:(NSString*)text andColor:(UIColor*)color andBeginTimeInSeconds:(int)seconds
{
    // Setup video layers
    CALayer *parentLayer = [CALayer layer];
    CALayer *videoLayer = [CALayer layer];
    parentLayer.frame = CGRectMake(0, 0, videoComposition.renderSize.width, videoComposition.renderSize.height);
    videoLayer.frame = CGRectMake(0, 0, videoComposition.renderSize.width, videoComposition.renderSize.height);
    [parentLayer addSublayer:videoLayer];

    // Create and add watermark layer
    CALayer *exportWatermarkLayer = [self watermarkLayerForSize:CGSizeMake(300, 300) andText:text andColor:color andBeginTimeInSeconds:seconds];
    exportWatermarkLayer.position = CGPointMake(videoComposition.renderSize.width/2, videoComposition.renderSize.height/4);
    [parentLayer addSublayer:exportWatermarkLayer];

    // Merge layers
    videoComposition.animationTool = [AVVideoCompositionCoreAnimationTool videoCompositionCoreAnimationToolWithPostProcessingAsVideoLayer:videoLayer inLayer:parentLayer];
}

用法：

AVMutableVideoComposition *videoComposition = [AVMutableVideoComposition videoComposition];
    videoComposition.instructions = instructions;
    videoComposition.renderSize = outputSize;
    videoComposition.frameDuration = CMTimeMake(1, 30);

    [self addWatermarkWithVideoComposition:videoComposition withLabel:@"Tag" andColor:lastColor andBeginTimeInSeconds:0];
    [self addWatermarkWithVideoComposition:videoComposition withLabel:@"Tag" andColor:lastColor andBeginTimeInSeconds:3];
    [self addWatermarkWithVideoComposition:videoComposition withLabel:@"Tag" andColor:lastColor andBeginTimeInSeconds:5];

AVAssetExportSession *exporter = [AVAssetExportSession exportSessionWithAsset:composition presetName:preset];
....................

我做错了什么？

Answer 1

据我所知，您的代码中有三个问题。您可能需要：

将... = NO;.

• Change fadeAnimation.removedOnCompletion = YES;更改为fadeAnimation.fillMode = xyz;，以便将您要导出的所有CALayers和所有CAAnimations的.beginTime与当前包含beginTime == 0.0的CAAnimations一起导出(这是默认值！！)转到AVCoreAnimationBeginTimeAtZero.

关于这一点的更多细节可以在苹果的AVVideoCompositionCoreAnimationTool文档中找到。

在CAMediaTiming协议的beginTime属性的苹果文档中也没有提到beginTime提示，这是不好的。

我也遇到过类似的问题，只有那些动画有效，我显式地设置了一个(非零) beginTime。希望这也是你的问题的解决方案。

Answer 2

我使用下面的代码来创建一个水印CALayer到视频的中心，它在osx Cocoa上工作。希望这能对你有所帮助。

- (CALayer *)createLayerImage:(NSString *)imagePath videoSize:(CGSize)videoSize
{
    CALayer *watermarkLayer = [CALayer layer];
    NSImage *watermarkImage = [[NSImage alloc] initWithContentsOfFile:imagePath];
    [watermarkLayer setContents:watermarkImage];
    [watermarkLayer setFrame:CGRectMake((videoSize.width-watermarkImage.size.width)/2,
                                        (videoSize.height-watermarkImage.size.height)/2,
                                        watermarkImage.size.width,
                                        watermarkImage.size.height)];
    NSLog(@"watermark layer %fx%f", watermarkImage.size.width, watermarkImage.size.height);
    CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
    animation.fromValue = [NSNumber numberWithFloat:1.0];
    animation.toValue = [NSNumber numberWithFloat:1.0];
    animation.removedOnCompletion = NO;
    animation.duration = 5.0;
    animation.repeatCount = 1;
    animation.beginTime = AVCoreAnimationBeginTimeAtZero;
    animation.fillMode = kCAFillModeForwards;
    [watermarkLayer addAnimation:animation forKey:@"opacity"];

    return watermarkLayer;
}