AVSynchronizedLayer sublayer animations that don't match the timing of movie

I'm using an AVSynchronizedLayer to animate a CALayer's position along a path. Since the timing of the layers is matched to the A开发者_开发知识库VPlayerItem, the layers correctly track an item in the video as it's playing.

What I'd like to do is also have a separate opacity/rotation animation on the layer, but I want it's timing to be independent of the video. Is there any way to override this?

The only way to do this was to animate the opacity/rotation manually using a CADisplayLink and interpolating the values without using Core Animation.

startTimestamp = CACurrentMediaTime();
CADisplayLink *displayLink = [CADisplayLink displayLinkWithTarget:self
                                                         selector:@selector(animate:)]
[displayLink addToRunLoop:[NSRunLoop currentRunLoop] 
                  forMode:NSDefaultRunLoopMode];

...

- (void)animate:(CADisplayLink *)link {    
    float duration = 1.0;
    float dt = (link.timestamp - startTimestamp) / duration;

    // Done?
    if (dt > 1.0) {
        [link invalidate];
        return;
    }

    // Disable CoreAnimation implicit animations
    [CATransaction begin];
    [CATransaction setDisableActions:YES];
    layer.opacity = dt;
    [CATransaction commit];
}