MIDI (Musical Instrument Digital Interface) files are digital files that generate synthesized music by combining various notes, sounds and effects. They are commonly used for accompaniment, composing, editing and arranging music. MIDI files contain instructions for executing sound events through a synthesizer or MIDI player (as opposed to storing the sounds themselves), so they are much smaller than digital audio files such as M4A, which have the capacity to stream high-quality audio. Converting an M4A file into MIDI is called music recognition. It's a fairly uncommon, complex process, but with the right program, you can do it yourself.
Choose a file converter program: WidiSoft Recognition System, Akoff Music Composer and Intelliscore Ensemble are all programs that let you convert audio files to MIDI files. (See Resources.)
Download the file converter program of your choice. Many programs are available as a free trial, but you may choose to purchase the program. Please note that not all audio conversion programs give you the option of converting into MIDI, so read descriptions carefully.
Open the converter program on your computer. Though program interfaces vary slightly from each other in design and function, most have a single main window with buttons or drop-down menus with various file conversion options.
Add the files you would like to convert by clicking "File," then "Add File," or the "Add" or "Add Files" button. In some programs, you can also drag and drop the files into the main window and add more than one file at a time.
Click the "Convert" button. In some cases (i.e., if you're using Intelliscore), you'll need to first convert the M4A file into an MP3 before converting it into MIDI. Files should take no more than a few minutes to convert.