What encryption/decryption system should I use for media server
"but it really doesn't discuss the part of users not able to decrypt the files using other tools." ... yes it does, because it discusses key management. As by Kerckhoffs principle, you should not try and secure the algorithm itself, security relies on the keys. Tools that receive the correct keys should be able to decrypt the media.

You can of course embed a secret or private key in the app, and require both the keys from the discussed scheme and the app key. It would however just take a single reverse engineering of the app to nullify the additional protection.

The practical way on how keys can be protected on the specific devices (e.g. using device specific key stores) is off topic for this site.