Smallest Video Format

I was wondering what the smallest video format is, or if they are all the same. Cuz i have an Ipad and want to put a couple of movies and there, but want to save space. Thanks in advance!

X264 (mini-mkv) is the smallest for good quality. I always try to use it. You can find it mostly on anime sites, but there are converters for it too. Just search for an x264 converter and you'll get one.

Sweet thanks