Here’s how I downloaded all the songs from a youtube playlist as mp3 files. You need to have youtube-dl instaled (I just used brew install youtube-dl)

First you need the playlist Id, it’s in the URL of the playlist, then visit a url like this:

https://developers.google.com/apis-explorer/?hl=en_US#p/youtube/v3/youtube.playlistItems.list?part=snippet&maxResults=50&playlistId=PL-ODR7uRLzL8VgaHR6S6h4KIkpNXUoccL&_h=1&

Then cmd-a, cmd-c to copy the whole page.

pbpaste | fgrep 'videoId":' | cut -d '"' -f 4 | while read fil; do youtube-dl -x --audio-format mp3 https://youtu.be/$fil; done

bam! all files downloaded!