I see the native camera app encodes videos (including 240 fps videos) at fixed frame rate but with AVFoundation no matter I use AVAssetWriter or AVCaptureMovieFileOutput I always endup with a variable frame rate video. This causes problem when you slow down a 240 fps video. Is it possible to mimic the behavior of native camera app ? I am anyways setting the minFrameDuration and maxFrameDuration to same value but it still doesn't help !