I've been trying for a while to figure this out on my own, I have scoured the internet and I cannot find any way to do this, I know how to get into the asset files but I don't exactly know what kind of ' file ' or stuff like that in to play music/videos, and I've heard sometimes you need to run the game as Administrator, but that I also do not know how to do. If anybody could help me out it would be much appreciated!

MP4 for TVs, MP3 for Radio. Just put them in the respective folder and it should work, if the file isn't broken in some way.

I never had to run in administrator mode but if you do the way to do it is right click on the exe and then click "run as administrator".

do also make sure to plug in the TV using the cord on the back of it, in the latest update they added a cord at least to the small TV, unsure about the others though