Exporting CALayer with implicit animation via AVExportSession

Question

I'm trying to export an animation for my custom CALayer with a custom property via AVExportSession, please find the setup below:

class CustomAnimatable: CALayer
{
    @NSManaged var brightness: CGFloat

    override init(layer: Any) {
        super.init(layer: layer);

        if let l = layer as? CustomAnimatable {
            self.brightness = l.brightness;
        }
    }

    override func action(forKey event: String) -> CAAction?
    {
        if event == "brightness" {
            let animation = CABasicAnimation(keyPath: event);
            animation.fromValue = presentation()?.brightness ?? self.brightness;
            return animation;
        }

        return super.action(forKey: event);
    }

    override class func needsDisplay(forKey key: String) -> Bool
    {
        if key == "brightness" {
            return true;
        }

        return super.needsDisplay(forKey: key);
    }

    override func display()
    {
        print("\(self) \(presentation()?.brightness) \(self.brightness)")
    }
}

Here's the export session pre-setup:

func render()
{
     ......

    let parentLayer = CALayer();
    let videoLayer = CALayer();
    let animationLayer = CustomAnimatable()

    parentLayer.frame = frame;
    videoLayer.frame = frame;
    animationLayer.frame = frame;

    parentLayer.addSublayer(videoLayer);
    parentLayer.addSublayer(animationLayer);

    CATransaction.begin()
    CATransaction.setAnimationDuration(2.2);
    CATransaction.setDisableActions(true);
    CATransaction.setAnimationTimingFunction(CAMediaTimingFunction(name: kCAMediaTimingFunctionLinear))

    let anim = CABasicAnimation(keyPath: "brightness");

    anim.fromValue = 1.0;
    anim.fillMode = kCAFillModeBoth;
    anim.beginTime = AVCoreAnimationBeginTimeAtZero;
    anim.repeatCount = 1;
    anim.toValue = 0.0;
    anim.isRemovedOnCompletion = false;

    animationLayer.add(anim, forKey: "anim")

    CATransaction.commit()


    let videoComposition = AVMutableVideoComposition();

    videoComposition.renderSize = CGSize(width: width, height: height);
    videoComposition.instructions = [mainInstruction];
    videoComposition.frameDuration = CMTimeMake(1, 30);
    videoComposition.animationTool = AVVideoCompositionCoreAnimationTool(postProcessingAsVideoLayer: videoLayer, in: parentLayer);

     ....
}

The issue is that the brightness value in the resulting video goes from 1 to 0 without animation. If I attempt to animate CALayer's native properties, e.g. opacity - the exported animation video is totally fine, the opacity smoothly fades from 1 to 0.

Am I doing it wrong for custom property?

Things I've considered:

• wrapping the explicit animation into CATransaction to disable implicit actions
• setting animation begin time to AVCoreAnimationBeginTimeAtZero and isRemovedOnCompletion to false as per "Editing Media with AV Foundation" session (Core Animation Gotchas section)

I'm a bit confused by the fact that native CALayer properties animate fine, thus the export session setup seems to be correct.

Besides that, if I add the custom layer to a view and animate the brightness property - it also animates fine. So the issue seems to be specific to rendering custom property animation w/ AVExportSession.

Answer 1

I'm not entirely sure why you have added both class videoLayer and animationLayer in parentLayer?.

parentLayer.addSublayer(videoLayer);
parentLayer.addSublayer(animationLayer);

Use following code Hope will helpful to you!

parentLayer.addSublayer(videoLayer);
videoLayer.addSublayer(animationLayer);