MIDI file format

MIDI files contain MIDI messages, along with timing information.

This page describes MIDI files, but the MIDI messages themselves are out-of-scope.

See the MIDI messages page to learn more about them.
See the MIDI hardware interface page for what happens inside a physical MIDI cable.


Extension	`.mid`
MIME type	`audio/midi`

Example MIDI file#

Bytes	Δt	Message
`4D546864 00000006`		Header chunk start : length = 6
`0001`		→ track_format = .simultaneous_tracks
`0003`		→ num_tracks = 3
`0180`		→ time_config = { .ticks_per_quarter_note, 384 }

`4D54726B 00000050`		Track chunk start : length = 80
`00 FF03 09`	0	`.sequence_or_track_name` (9 bytes) : `"SomeTitle"`
`536F6D655469746C65`
`00 FF01 09`	0	`.text` (9 bytes) : `"creator: "`
`63726561746F723A20`
`00 FF01 1E`	0	`.text` (30 bytes) : `"LilyPond 2.24.2 "`
`4C696C79506F6E6420322E32342E32`
`202020202020202020202020202020`
`00 FF5804 04 02 18 08`	0	`.time_signature`
`00 FF5103 0F 42 40 98`	0	`.set_tempo`
`00 FF2F 00`	0	`.end_of_track`

`4D54726B 0000005A`		Track chunk start : length = 90
`00 FF03 06`	0	`.sequence_or_track_name` (6 bytes) : `"upper:"`
`75707065723A`
`00 C0 0C`	0	`.program_change` : SoundSet.marimba (`0C`)
`00 C0 0C`	0	`.program_change` : SoundSet.marimba (`0C`)
`00 FF04 07`	0	`.instrument_name` (7 bytes) : "marimba"
`6D6172696D6261`
`00 FF59 020000`	0	`.key_signature` : TODO

`00 903C5A`	0	NoteOn(C₄, v=90)

`8300 903C00`	384	NoteOn(C₄, v=0)
`00 90405A`	0	NoteOn(E₄, v=90)

`8300 904000`	384	NoteOn(E₄, v=0)
`00 90435A`	0	NoteOn(G₄, v=90)

`8300 904300`	384	NoteOn(G₄, v=0)

`8300 903C5A`	384	NoteOn(C₄, v=90)
`00 90405A`	0	NoteOn(E₄, v=90)
`00 90435A`	0	NoteOn(G₄, v=90)

`8C00 903C00`	TODO	NoteOn(C₄, v=0)
`00 904000`	0	NoteOn(E₄, v=0)
`00 904300`	0	NoteOn(G₄, v=0)

`00 FF2F00`	0	`.end_of_track`

`4D54726B 00000052`		Track chunk start : length = 82
`00 FF03 06`	0	`.sequence_or_track_name` (6 bytes) : `"lower:"`
`6C6F7765723A`
`00 C1 0C`	0	`.program_change` : SoundSet.marimba (`0C`) on channel 2
`00 C1 0C`	0	`.program_change` : SoundSet.marimba (`0C`) on channel 2
`00 FF04 07`	0	`.instrument_name` (7 bytes) : "marimba"
`6D6172696D6261`
`00 FF59020000`	0	`.key_signature` : TODO

`00 91305A`	0	NoteOn(C₃, v=90, channel=2)

`8300 913000`	384	NoteOn(C₃, v=0, channel=2)
`00 91305A`	0	NoteOn(C₃, v=90, channel=2)

`8300 913000`	384	NoteOn(C₃, v=0, channel=2)
`00 91305A`	0	NoteOn(C₃, v=90, channel=2)

`8300 913000`	384	NoteOn(C₃, v=0, channel=2)
`00 91305A`	0	NoteOn(C₃, v=90, channel=2)

`8300 913000`	384	NoteOn(C₃, v=0, channel=2)
`00 91305A`	0	NoteOn(C₃, v=90, channel=2)

`8C00 913000`	TODO	NoteOn(C₃, v=0, channel=2)

`00 FF2F00`	0	`.end_of_track`

Format details#

A MIDI file consists of one header chunk ("MThd") followed by one or more track chunks ("MTrk").

Track chunks ("MTrk")#

A track chunk starts with "MTrk" + length:

4D54726B    "MTrk"
0000ABCD    u32 -> length of the remainder of this chunk

...which is followed by one or more events.

Each event consists of a time delta (in ticks) plus the raw bytes of a MIDI message.

The last event must be an .end_of_track MIDI message (FF2F00).

Header chunk ("MThd")#

Header chunks contain three things:

pub const Header = struct {
    track_format: TrackFormat,
    num_tracks: u16,
    time_config: TimeConfig,
};

Example#

4D546864    "MThd" (chunk type)
00000006    u32 -> len = 6
    0001    u16 -> track_format = TrackFormat.SimultaneousTracks
    0003    u16 -> num_tracks = 3
    E728    u16 -> time_config = TimeConfig.withMillisecondTicks()

TrackFormat #

u16	Enum	JSON
0	`.one_track`	`"one_track"`
1	`.simultaneous_tracks`	`"simultaneous_tracks"`
2	`.independent_tracks`	`"independent_tracks"`