The concept of repeatable music is an old thing, most obviously used in video games, where you need to loop the same track over and over. There are a lot of tools and music formats out there to handle this. The tracker formats: mod, s3m, it, and so on, are designed to allow infinitely looping music. It was easy to loop music with any basic sound chip: the Commodore 64’s SID, Ad-Lib’s YM3812, or the IBM PC Speaker.
But there’s no clear standard out there for looping rendered music. Andy Church put together mp3play.pl, which relies on an ID3v2 comment inside of a MP3 file to loop based on the location of sample offsets:
repeat start=X len=Y
But so far as I can tell, this was just arbitrary and not supported by any major MP3 player out there.
As far as I know, there’s no standard out there for looping rendered music. Maybe I’ll discover one some day, and when I do, I’ll note it here.