(Since my developing skills are near zero, so eh…)
Basically, a music player that converts (any sort of tune) into a chiptune (in real-time?) and plays it. Various sound sets can be chosen – from 8 bit ones, to 16 bit… super mario (snes) sound set, etc. Bonus points if its CLI, made using c++ code.
Here’s an XKCD describing the development situation you just described.
Converting audio into a different set of tunes, especially if they have multiple layers, is ridiculously difficult. There already exists MIDI converters online a google away that can create chiptune-esque arrangements from input songs but they SUCK, doing nothing more than trying to match input frequency averages to the target frequency of every midi note. But just asking someone to create an app (let alone a free open source one) that could make a usable chip tune with the slightest awareness of its input tunes is a very very tall order and this is not the right community to be asking it.