Doing a quick search for "mp3 to midi converter", I see several. I don 't know how well any of them work, though. I usually use midi a bit differently, to record keystrokes and dynamics from my midi keyboard, so I don't have a lot of use for that sort of converter.
But looks like there's some free ones you can give a try.
I used to have a bit of software for guitar that would output midi from a standard electric guitar, but I didn't feel it worked well enough to use much. It could only do single note melodies, no harmony/chords, and even then you had to play kinda slow.
That was years ago, though, and they likely have such things working better by now.
"This young wine may have a lot of tannins now, but in 5 or 10 years it is going to be spectacular, despite the fact that right now it tastes like crude oil. You know this is how it is supposed to taste at this stage of development." ~ Itzhak Perlman
MP3 doesn't translate well to midi. Midi is synth music,which means it tells the computer the instrument and the notes to play and the computer synthesizes it. Think of it as the computer reading a score and reproducing it.
As for MP3, it's a digital, compressed form of sound waves compressed into a single track. It's hard to get different sounds from a single track and turn it into synth music.
There are programs that make it, but they are mostly terrible. Take a look in the .mid I attached, it's been "translated" from an MP3 to a .mid file. Here's the original:
The program I used is called "Intelliscore", btw. Since that is a quite simple song, I suggest you try to learn it by ear.
Skype: augustoad Email: [email protected] Phone number/whatsapp: +55 42 9861-4084. I'd be happy to talk anything fiddle-related to anyone! :)