Getting VR to work on ps4 Media Player

Hey,

Downloaded some VR mp4s from a VR paysite, which they say should work with ps4VR (standard - non-pro). I'm using a 32 GB USB - however, while I can see the file in media player I get the msg 'cannot play the media'. Their tech help have advised that the videos should work (and work for them). I've tried both FAT32 and exFAT for the file system, but no luck.

Currently using Littlstar, which works, but requires a subscription, so I'd prefer Media Player ongoing.

Does anyone have any experience with this?

Thanks in advance