In terms of MIDI software, there are many varietions, such as software that put importance on real-time function, play function only, or software that let users to input from MIDI controller and so on. If you are to create music software that deals with MIDI, the module that processes MIDI will be needed. I recommend that you create this part separately and independently from the software itself. For example, in case of using VC++, you will need to prepare a class that deals with playing MIDI files or playing by MIDI.