Adding mp3 files to Brave Playlist

Earlier today, I started experimenting with the Brave Playlist feature and was extremely impressed with the ability to put all my music into one place and listen to it offline AND in sleep mode. YouTube videos can be a bit bulky, though, so I tried to download the MP3 file at this website and add it to my Brave Playlist:

Unfortunately, I could not do so, and the only thing my Brave Playlist could pick up was the embedded YouTube video. While I could download the MP3 separately, I could not add it to my playlist. Is there a way to do this that I am unaware of? If not, could this feature be added in the future? Thank you!