I have enough songs I could listen to a different song constantly for the next 10 years.
Granted, some of the mp3s I have are a couple hours long, but hey its still only one.
I have different playlists depending on the mood I am in.
I even have a Friday Night playlist.
Every two years I play every single song non-stop till the end of my collection.
I have an app that records the song to my last.fm profile.
Starting Jan 1 2020 I will be scrobbling my collection again.
Last.Fm takes my scrobbles and gives me reports that tell me different things about my collection.
It then recommends new artists plus it offers me a chance to play my radio which is an assortment of the music I play the most.
Last.FM is free.
http://www.last.fm/user/tomishereagain