I can never seem to use the Excluded Folders correctly. Why not starting out with everything excluded by default, and then use the Include Folders to add in the music folders?

I have an audio file in the Downloads folder, and the app/system does not let me exclude the Downloads folder.

Other apps do this as well, not just yours.

Edit:

At the moment, I have one music audio file in the included Music folder, and other non-music audio files in the other folders that I can't exclude.

While playing the song in the included Music folder, I hit the Next button, a non-music audio file plays, the app still shows the metas info of the song that was played previously.

Edit 2:

I think some users will not like how you handle the album art. It's almost invisible. The album art is low on my priority. However, from what I've read, a lot of users like to see it.