Right now I have a script that uses cp to copy newly added media files to a second, identical drive in another room as a backup. there has to be a better way to do this.

I would use rsync. It can be told exactly what kind of updates are needed from many different criteria, including modified time and file hashing. This is likely what you want.

I sometimes use git as a form of backup, particularly my writing, that I push to remote locations. Its great for text, but not so much for already compressed media.

Finally, I also use syncthing (which is a full program, not a CLI tool) to keep several machines synced up. There are many file versioning options and encryption that can be set independently on each machine.