It looks like it requires a MIDI which it then converts to sound like it’s coming out of a Gameboy.
Here’s what the FAQ says:
> How it works
>
> Search a song, pick a MIDI source, hit Generate. The Wario Synthesis Engine analyses the MIDI and resynthesises it using Web Audio oscillators tuned to mimic the Game Boy's 4-channel sound chip. All processing runs in your browser.
Here’s what the FAQ says:
> How it works
>
> Search a song, pick a MIDI source, hit Generate. The Wario Synthesis Engine analyses the MIDI and resynthesises it using Web Audio oscillators tuned to mimic the Game Boy's 4-channel sound chip. All processing runs in your browser.