If you’re unfamiliar with Envato’s Music Kits, read Eric Schwarz’s tutorial Why Envato Music Kits Are the Essential Audio Solution to Any Project.
Unlike the typical music item that is usually a fixed-length track, Music Kits are song tracks that have been pre-edited into individual musical sections that can be rearranged, like building blocks, to create custom-timed and custom-structured pieces.
This means that, without musical or audio expertise or highly specialised audio software, you can create a professional finish to your soundtracks by dragging and dropping individual song sections to fit both the length of music your scenes require and the tempo progression needed.