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.