how to add mobile disk space for ipod touch?

If the files do not fit you will need to work out how to stream them - that will depend on where the files came from & if you have reliable hosting & fast internet etc.

I assume you have the files in iTunes on a computer, if that is the case consider enabling the option to sync SD movies (set in the 'Summary' options when syncing). If you are lucky these files will contain a HD & SD version that can allow them to sync. The App store may have the option to download SD versions if these are purchased there, try looking in your purchase history for that if the Files are HD. Get Info on each file to examine that.

Otherwise try selecting the files in the iTunes TV Shows list & attempt to create a new version via the 'File menu > Create iPhone/ iPod version'. It may reduce the size sufficiently to cram them onto the device.

iTunes store purchases cannot be converted due to the DRM.

Also consider removing apps & other files to make room, assuming they are less important compared to the videos.

iOS lists the storage used under the 'Settings app > General > Usage > Manage storage', see if that gives you ideas what to clear out.

P.S. I believe the 'Camera Connection Kit' can play movies stored on SD cards, but I have not experienced that - it may only work with non iTunes store purchases (gotta love DRM). Search here for note, I'm sure others have discussed this. It may be a way to workaround it?

The camera Connection kit only works with iPhones and iPads, not iPod touches.

You can get wifi enabled external HD like:

http://www.wdc.com/en/products/products.aspx?id=1330

http://www.cnet.com/topics/storage/best-hard-drives-and-storage/best-mobile-wire less-drives/

You have to use an app o the iPod to access the wifi HD and I do not think that it will play Apple DRM protected media.

OR something more compact like these.

https://www.sandisk.com/home/mobile-device-storage/ixpand

OR

https://www.sandisk.com/home/mobile-device-storage/connect-wireless-stick

With both these drives, you cannot stream iTunes movie content directly from these drives, but you can transfer/copy the video content from the drive to the iPad to play from the iPad.

This will, also, be true of portable WiFi hard drives. You won't be able to stream the iTunes movie content from the external drive, but you should be able to transfer/copy it to the iPad to play from the iPad.

During iOS 8 updates, Apple secretly, covertly and underhandedly remove the ability to be able to stream purchased iTunes video content from any external storage sources.

Good Luck!