iDevices and iOS could never use standard, conventional external hard drives.
The power supplies in iDevices and iPads, specifically, are simply not powerful enough to handle these standard computer peripheral external storage devices.
There are a few special storage devices for mobile devices. There are portable, bulit-in WiFi hotspot hard drives for mobile devices made by Western Digital and Seagate.
There are special mobile lightning connected and built in WiFi Hot spot, USB flash drives made by SanDisk (now owned by Western Digital)
This listing maybe incomplete and somewhat outdated, now. So do an online search for similar external data storage devices for iPads
Kingston Electronics makes some data storage devices for iPads/iDevices, now, too!
Besides, if these ARE purchased iTunes TV/movie content, you cannot stream/play these movies from any mobile external storage sources any longer, anyways.
The iTunes TV/Movie content will ONLY play if it is, physically stored on the iDevice.
So, you might as well just re-download your purchased iTunes content from the iTunes app on your iPad and gets stored in your TV App under either Library, TV Shows OR Movies.
You used to be able to stream iTunes purchased TV/Movie from mobile wireless storage drives, but Apple, rather secretly and covertly, coded this ability out of iOS sometime during the course of updates in iOS 8, four years, or so, ago.
This ability used to work in iOS 5 through iOS 7, but secretly disappeared after the introduction of iOS 8 with no warning or clue from Apple.
This is THE ONE HUGE reason I no longer purchase TV/Movies from Apple iTunes, any longer and have gone back to purchasing movies and TV Shows on physical, multi-format discs, now.
I can do what I want with these purchased discs and have been able to create versions I can put on my special mobile Wireless hard drives/flash drive and can NOW stream my purchased TV shows and movies once again from my remote storage drives without having to eat up my iPad physical storage with storing movies on it to play.
I have a a collection of my favorite movies saved on a 128 GBs SanDisk mobile rechargeable wireless, Wifi hot spot built-in flash drive that I can just put into a clothes pocket and stream my movie collection from it to my iPad using an iOS SanDisk app on my iPads.
My 1st generation, 2010 iPad 1, running iOS 5.1.1,can still stream all of my purchased iTunes movie/TV content from my Seagate Wireless hard drive, but this is the ONLY iPad that can.
Apple isn't going back through iOS 5-7 just to modify the code to code this remote external drive streaming out of these older iOS versions.
So, Good Luck to You!