The DUET engine in a page of your own: duet-web.js + duet-worklet.js + duet.wasm, three files beside your page and one class. This is the whole of it — view the source. The full player is the same class with a page around it.
duet-web.js
duet-worklet.js
duet.wasm
▶ PLAY THE CO-PLAY DEMO ■ STOP ‖ PAUSE or your own: