Here are the technical details:
There are only 12 sampled notes (the rectangular waveforms) and three parts / clouds – the moving circle things. The strings part on the right is cycling through three pairs of two-note chords. Top left are three cycling notes on trumpets, bottom left are three cycling notes on trombone / tenor sax.
Because the three cycles are slightly different lengths and not synchronised in any way, you get the illusion that the piece is constantly evolving – even though it isn’t really – it just takes quite a long time for it to repeat as a whole, even though the three parts themselves aren’t very long. So I call it “semi-generative” music.
I used NI Session Strings and NI Session Horns to produce sustained single notes then imported them into Borderlands and recorded the parts’ motion that you’re watching now.