Conversion with fixed # of frames
extract the frames as rawvideoffmpeg -i input.mov -f rawvideo -b 50000000 -pix_fmt yuv420p -vcodec rawvideo -s 1920x1080 -y temp.rawrecreate the video with new framerate
ffmpeg -f rawvideo -b 50000000 -pix_fmt yuv420p -r 24 -s 1920x1080 -i temp.raw -y output.mov
Conversion with fixed running length
ffmpeg -i input.mov -sameq -r 24 -y output.mov