The longest recorded song is "Longplayer" by Jem Finer, a British musician. - Apparently.
Longplayer is an infinite composition that began playing on December 31, 2000, and will continue to play until December 31, 2999. The piece is a series of random musical phrases that are generated by a computer program, creating an ever-changing soundscape. According to the Longplayer website, the song has been playing continuously for over 22 years, with a total duration of approximately 637,000 hours.