Ask HN: Best way to create a Reverse Karaoke Engine?

Basically, I want to interleave musical notes and vocals. I want to take the vocals, apply pitch correction and then appropriately add guitar, piano ,drum and other instruments harmoniously. Not in a preset way. What is the best way I can approach going about building this. Most of the software for music don't have APIs or command line interface. They are executables that run on the computer.