Convert mp4 to avi while keeping frame rate and quality and being able to play in QuickTime?
An AVI file is just a container and can contain any codec, so if you want to encode to QuickTime and Media player, you need to:

ffmpeg -i input.mp4 -c:v libx264 -c:a libmp3lame -b:a 384K output.avi


and above means:


Use the h264 Codec which both QT and WPlayer can display nowadays
use 384 Kbps MP3 encoding for audio


don't touch anything else like frame rate, resolution, ... and copy these as is.