The file extension for MIDI Files is: .MID
A MIDI File is a 'data file'. That is, there are no sounds or audio contained in the MIDI File , just a digital set of instructions. The MIDI File data is sent to a receiving sound source like a MIDI File Player (such as the MERISH PLUS, X-Light) or through software based MIDI sequencing programs like Sonar and Cubase (for PC) and Logic, GarageBand and Pro Tools for Mac.