How do you convert an aac file to a midi file

MIDI Files can be converted into an AAC file but an AAC file cannot be converted to a MIDI File.

MIDI Files are data files made up of different instrument sounds assigned to a MIDI channel. The sounds (instruments) are always separate and can be individually edited.

AAC song files are an 'Audio' File - like a song you would hear on a CD or an MP3. These files cannot be converted to MIDI Files as they are a 2 channel audio file. The easiest way to explain this is:

You want to bake a cake. The completed cake will be the AAC file (or an MP3, WAV file etc..). The flour, eggs milk and other ingredients that are going into the cake are the individual instruments, like Drums, bass, guitars, keyboards and so on.

At this stage, you have the means to create a MIDI File because the individual parts are separate from the whole (cake). However, once the ingredients are mixed and baked, then the cake is whole and the individual parts that went into the cake no longer exist. In short, there's no turning back once the audio file is recorded and saved in the audio format (AAC, or MP3, WAV etc).