Using an External HD to watch apple movies on iPad

I have downloaded a my a lot of my movies on an external HD. Right now there is no issue with playing these movies that I have downloaded from my computer to an external HD and play them on my computer when I do not have internet, like on a flight. what I'm trying to do now is, just use that same external HD and play the movies on my iPad. I dont see a difference in using my computer or my iPad. both are registered to me.