DVD player will not play the videos on my Passport SE?

My son is in Afgan and wanted to play videos from my passport se 1TB drive but says get this usb not recognised?  Seen something about formatting but not sure what to do and if this is correct.  We have sent him the portable dvd player and he says he can play dvd on it from someones external drive??  What cant we do it from My Passport Essential SE?  Can anyone help please.

What is he trying to play the videos on a compuer, Play Station, TV? His playback device will determine what fromat you need. Ask him to find out how the other drive that works is formatted possibly FAT32 or NTFS (standard for Windows).