Why using midi
Let me explain it. MIDI/KAR and WAV/MP3 files have completely different essence. MIDI file just contains notes like notes on note greed. It some thing like text. It designed specially for visualization and composing of music. KAR it something like MIDI but with embedded lyrics. It designed specially for “karaoke”. But wave (WAV) files are completely different. They contain acoustic wave, which consists of air pressure, during many small time periods. For example one second of wave with quality 22050 KHz contains 22050 sequencing samples of air pressure. It some thing like picture. It designed for represented of physical acoustic processes in digital form. MP3 it is compressed WAV files. Designed for saving disc space. Usually it decreases file size in 10 times. Conversion from MP3 to MIDI it not a just changing file format but difficult problem. It something like converting picture to text (text recognizing). And like for text recognizing not any picture can be recognized as text. But you always can try.
So for notes pitch representation we need MIDI or KAR files. Because only them contains notes.