Modular Music is a series of music assets which can be used to play music dynamically in a game, by having each track split up into several parts.

https://w.soundcloud.com/player/?url=https%3A//api.soundcloud.com/playlists/1510817680&color=%23e1793d&auto_play=false&hide_related=false&show_comments=true&show_user=true&show_reposts=false&show_teaser=true

The following three battle tracks are split up into an intro, an outro and several variations in intensity.

Each zip file contains a text file describing the rhthmic properties of the track.

Using Godot Engine?

If you are using Godot, consider using this free addon (this music was developed with this addon in mind).