Thank you for your reply. I did implement it as suggested, and for the most part it works great. However, I believe I found a problem and potential bug when a UIViewPropertyAnimator is configured in didMoveToWindow in a view that is being presented in a popover. This bug can be reproduced in the following example code: https://github.com/tcwalther/PropertyAnimatorPresent/tree/29812e53a8b6d413a156d26de3fe3c01792df9a9 In this code, there are two view controllers. The first one contains a button that presents the second view controller as a popover. The second view controller contains one view of type AnimatedView. The AnimatedView has a UIViewPropertyAnimator that is being configured on didMoveToWindow. When that configuration is called, the property animation works fine, but the popover presentation animation is broken. Have a look at the following screenshots: Can you advise me how to fix the popover animation?

Thanks, I didn’t know about AVAssetWriter. I‘ll try it out. On a first glance, movieFragmentInterval looks like it’s only relevant for QuickTime, not MPEG. However, shouldOptimizeForNetworkUse should do the trick - that should put the moov atom at the beginning of the container. I‘ll report back once I tried it. Edit: accidentally posted this from my private apple Id but I‘m the OP