Let's imagine we have a lot of mp3 files ( forexample one of the pluralsite courses converted to mp3 ).
URL=https://www.pluralsight.com/courses/run-effective-meetings
PASS=pass
USER=user
OUTPUT="%(playlist_index)s. %(title)s-%(id)s.%(ext)s"
youtube-dl --username $USER --password $PASS -o $OUTPUT --extract-audio --audio-format mp3 $URL