This is the source to VGMTool, my first ever C/C++ project! Thus, it is full of horrors. I am slowly modernising it and converting to mild C++20.
See https://www.smspower.org/Music/VGMs for VGM music and https://www.smspower.org/Music/HowToMakeVGMs for some information on how to use VGMTool.