AI can probably do it if you can find the right AI. Or you might have to wait 'till tomorrow since AI gets smarter every day!
There are audio-to-MIDI converters and once you have MIDI you have the notes & timing. You'd have to search and they don't always work perfectly. Chords and multiple instruments make if more difficult. From what I've read Melodyne is the best but it starts at $100 and I have no idea if the cheap version has that capability.
Interesting, why not go for it? I never heard of this lol. Now I might just do especially if this is so complex to convert to Arduino Melody format.
I see this DFPLAYER uses UART to communicate, sadly I have 1 single pin left on my micro, I assume it's enough if I send commands to it for the RX wire.