The only file types I've gotten to work are mp3s for radio, mp4 for video and png for photos.

I've been trying to find out if there are any ways or plans to get FLAC, jpg or other file types available ingame in the future. I just really want some FLAC support. Does anyone know if there is something I can do about that right now?

There are hints in the game menu, maybe they will help you

i wish there was mkv support tbh, got the entire KOTH series but its all MKV

You're kind of SOL on that unless the dev adds more file types.

While it would be nice to have those, i can understand why the dev chose mp3 and mp4  since they are a widely used file format that don't take up much space nor need any extra things to run it natively. The only gripe i have with it though is that it doesn't support newer MP4 codecs (such as h.265) which some websites use, and can stop the video from being played correctly.

Here's to them possibly revamping the player, though, and hopefully expanding what files it can accept.