Question

I’m attempting to create a fairly simple CoreAnimation for use in an AVComposition. My goal is to create a CALayer which, through various sublayers, fades a title in and out, then fades in an out images. A slideshow, basically. This is being exported to a .mov using AVAssetWriter.

With help from the WWDC 2011 AVEditDemo, I’ve been able to get a title and images appearing. The problem is that they are all on screen at the same time!

I have created each layer with an opacity of 0.0. I have then added an CABasicAnimation to fade them from 0.0 to 1.0, using the following code:

CABasicAnimation *fadeInAnimation = [CABasicAnimation animationWithKeyPath:@"opacity"];
fadeInAnimation.fromValue = [NSNumber numberWithFloat:0.0];
fadeInAnimation.toValue = [NSNumber numberWithFloat:1.0];
fadeInAnimation.additive = NO;
fadeInAnimation.removedOnCompletion = YES;
fadeInAnimation.beginTime = 1.0;
fadeInAnimation.duration = 1.0;
fadeInAnimation.fillMode = kCAFillModeForwards;
[titleLayer addAnimation:fadeInAnimation forKey:nil];

The problem seems to be the ‘beginTime’ property. The “1.0” is meant to be a delay, so it starts 1 second after the start of the animation. However, it is appearing on the screen straight away. A fade out animation

The reverse of this code, for the fade out, simply changes the fromValue to 1.0 and the toValue to 0.0. It has a begin time of 4.0 and works perfectly.

I’m using the following to create the animatedTitleLayer:

CATextLayer *titleLayer = [CATextLayer layer];
titleLayer.string =self.album.title;
titleLayer.font = @"Helvetica";
titleLayer.fontSize = videoSize.height / 6;
titleLayer.alignmentMode = kCAAlignmentCenter;
titleLayer.bounds = CGRectMake(0, 0, videoSize.width, videoSize.height / 6);
titleLayer.foregroundColor = [[UIColor redColor]CGColor];
titleLayer.opacity = 0.0;

The image fade in animations have a beginTime 5 seconds apart. Like the title, their fade out animations work fine.

Any help would be greatly appreciated!

Cheers!

EDIT

The answers were all helpful, but ultimately I discovered that only one animation could be added to a CALayer. The fade out animation was working as it was the last one added.

I then tried a CAAnimationGroup, but this didn’t work as I was modifying the same key value path.

So I’ve realised that a CAKeyframeAnimation is the best for this. Only I’m having some difficulty with that too! The code is now fading in okay, but it isn’t fading out. I’ve tried various fillMode’s, changed the duration, etc. Can’t make it work!!

Here is my code:

    CAKeyframeAnimation *fadeInAndOut = [CAKeyframeAnimation animationWithKeyPath:@"opacity"];
    fadeInAndOut.duration = 5.0;
    fadeInAndOut.autoreverses = NO;
    fadeInAndOut.keyTimes = [NSArray arrayWithObjects:  [NSNumber numberWithFloat:0.0],
                                                            [NSNumber numberWithFloat:1.0],
                                                    [NSNumber numberWithFloat:4.0], 
                                                    [NSNumber numberWithFloat:5.0], nil];

    fadeInAndOut.values = [NSArray arrayWithObjects:    [NSNumber numberWithFloat:0.0],
                                                    [NSNumber numberWithFloat:1.0],
                                                    [NSNumber numberWithFloat:1.0], 
                                                    [NSNumber numberWithFloat:0.0], nil];
    fadeInAndOut.beginTime = 1.0;
    fadeInAndOut.removedOnCompletion = NO;
    fadeInAndOut.fillMode = kCAFillModeBoth;
    [titleLayer addAnimation:fadeInAndOut forKey:nil]; 

Answer 1

I’m faced the same issue and the problem is – one layer can’t contain fade in and out.
So you can add the other animation to the parent layer as i did

CALayer *parentLayer = [CALayer layer];
CALayer *animtingLayer = [CALayer layer];

//FADE IN
        CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
        animation.beginTime = CMTimeGetSeconds(img.startTime);
        animation.duration = CMTimeGetSeconds(_timeline.transitionDuration);
        animation.fromValue = [NSNumber numberWithFloat:0.0f];
        animation.toValue = [NSNumber numberWithFloat:1.0f];
        animation.removedOnCompletion = NO;
        animation.fillMode = kCAFillModeBoth;
        animation.additive = NO;
        [parentLayer addAnimation:animation forKey:@"opacityIN"];

//FADE OUT
        CABasicAnimation *animation = [CABasicAnimation animationWithKeyPath:@"opacity"];
        animation.beginTime = CMTimeGetSeconds(CMTimeAdd(img.passTimeRange.start, img.passTimeRange.duration));
        animation.duration = CMTimeGetSeconds(_timeline.transitionDuration);
        animation.fromValue = [NSNumber numberWithFloat:1.0f];
        animation.toValue = [NSNumber numberWithFloat:0.0f];
        animation.removedOnCompletion = NO;
        animation.fillMode = kCAFillModeBoth;
        animation.additive = NO;
        [animtingLayer addAnimation:animation forKey:@"opacityOUT"];

    [parentLayer addSublayer:animtingLayer];