I looked up a solution to the stuttering you get when you slow your footage. When you right click on a file you can access Time which is the place to make your footage faster or slower. this can cause a stuttering. To sort of solve, you right click again and go to Frame Blending and click on Pixel Motion. This smooths footage and make it look better. Make sure you render your frames before you move on to the next layer. See link to tutorial . https://www.youtube.com/watch?v=rzP6SurYoJw