Well, personally I don't you're going to succeed in converting an mp3 file into a midi file. If you find a way to do that let me know. There is a program at the bottom of that midi search engine page that converts wav files to midi supposedly. I'm not sure how well that actually works as I've never tried it.
Moreover, if there are vocals on the mp3 file I don't know how they would be converted into a midi. Seems to me that any such conversion would end up being a jumbled mess.
Now if you had a pure solo piano mp3 that might convert to a wav and then to a midi???
I'm not all that familiar with all the possibilities. I just convert midi files to sheet music.
Maybe someone else can offer you more information or better methods. I'm just offering my own limited knowlege for whatever it's worth.
