I made an App Store preview video using QuickTime player on OS X Yosemite.
When I try to upload the video to iTunesConnect, I get an error message:
The frame rate of your app video preview is too high.
Videos can be easily converted using ffmpeg, a handy tool that can be installed using homebrew.
ffmpeg -r 30 -i 60fpsvideo.m4v -vcodec copy -acodec copy 30fpsvideo.avi