A MID file is a standard MIDI (Musical Instrument Digital Interface) file used by music authoring and mixing programs as well as MIDI hardware devices. It contains music data, such as what notes are played, when they are played, how long each note is held, and how loud each note is played.
MID files are used to encode MIDI data into a standard format that is interoperable between different types of software programs and hardware devices. They may also contain controller data for a device. For example, a MID file can be used to change instruments on a MIDI hardware device or modify sustain pedal information.
MID files contain attributes of music data rather than music data itself. They can be played back using software instruments that interpret this data.