The format is similar to MIDI, in that it defines musical notes, and does not support sampledigital audio for sound effects. IMF files store the actual bytes sent to the AdLib's OPL2 chip, which uses FM synthesis to produce audio output. The format is based on the AdLib command syntax, with a few modifications. Due to the limited features and relatively low sound quality, modern games no longer use IMF music.
Once extracted from a game, IMF files can be played with special sound libraries which emulate AdLib cards. One of the most popular ones is AdPlug, which can be used, for instance, through its Winamp plugin.