The MIDI file format is used to store MIDI song data on disk. The discussed
version of the MIDI file spec is the approved MIDI Manufacturers' Associations
format version 0.06 of (3/88). The contact address is listed in the adresses
file. Version 1.0 is technically identical but the description has been
rewritten. The description was made by Dave Oppenheim, most of the text was
taken right out of his document.
MIDI files contain one or more MIDI streams, with time information for
each event. Song, sequence, and track structures, tempo and time signature
information, are all supported. Track names and other descriptive information
may be stored with the MIDI data. This format supports multiple tracks and
multiple sequences so that if the user of a program which supports multiple
tracks intends to move a file to another one, this format can allow that to
happen.
The MIDI files are block oriented files, currently only 2 block types are
defined, header and track data. Opposed to the IFF and RIFF formats, no
global header is given, so that the validation must be done by adding the
different block sizes.
A MIDI file always starts with a header block, and is followed by one or
more track block.
The format of the header block :
OFFSET Count TYPE Description
0000h 4 char ID='MThd'
0004h 1 dword Length of header data (=6)
0008h 1 word Format specification
0 - one, single multi-channel track
1 - one or more simultaneous tracks
2 - one or more sequentially independent
single-track patterns
000Ah 1 word Number of track blocks in the file
000Ch 1 int Unit of delta-time values.
If negative :
Absolute of high byte :
Number of frames per second.
Low byte :
Resolution within one frame
If positive, division of a quarter-note.
The track data format :
The MTrk block type is where actual song data is stored. It is simply a
stream of MIDI events (and non-MIDI events), preceded by delta-time
values.
Some numbers in MTrk blocks are represented in a form called a variable-
length quantity. These numbers are represented 7 bits per byte, most
significant bits first. All bytes except the last have bit 7 set, and
the last byte has bit 7 clear. If the number is between 0 and 127, it
is thus represented exactly as one byte. Since this explanation might not be
too clear, some exapmles :
Number (hex) Representation (hex)
00000000 00
00000040 40
0000007F 7F
00000080 81 00
00002000 C0 00
00003FFF FF 7F
001FFFFF FF FF 7F
08000000 C0 80 80 00
0FFFFFFF FF FF FF 7F
The largest number which is allowed is 0FFFFFFF so that the variable-
length representation must fit in 32 bits in a routine to write
variable-length numbers.
Each track block contains one or more MIDI events, each event consists of
a delta-time and the number of the event. The delta-time is stored as a
variable-length quantity and represents the time to delay before the following
event. A delta-time of 0 means, that the event occurs simultaneous with the
previous event or occurs right at the start of a track. The delta-time unit is
specified in the header block.
Format of track information block :
OFFSET Count TYPE Description
0000h 4 char ID='MTrk'
0004h 1 dword Length of header data
0008h ? rec <delta-time>, <event>
Three types of events are defined, MIDI event, system exclusive event and
meta event. The first event in a file must specify status; delta-time itself
is not an event. Meta events are non-MIDI informations.
The format of the meta event :
OFFSET Count TYPE Description
0000h 1 byte ID=FFh
0001h 1 byte Type (<=128)
0002h ? ? Length of the data, 0 if no data
stored as variable length quantity
? byte Data
A few meta-events are defined. It is not required for every program to support
every meta-event. Meta-events initially defined include:
FF 00 02 ssss Sequence Number
This optional event, which must occur at the beginning of a track,
before any nonzero delta-times, and before any transmittable MIDI
events, specifies the number of a sequence.
FF 01 len text Text Event
Any amount of text describing anything. It is a good idea to put a text
event right at the beginning of a track, with the name of the track, a
description of its intended orchestration, and any other information
which the user wants to put there. Programs on a computer which does not
support non-ASCII characters should ignore those characters with the hi-bit
set. Meta event types 01 through 0F are reserved for various types of text
events, each of which meets the specification of text events(above) but is
used for a different purpose:
FF 02 len text Copyright Notice
Contains a copyright notice as printable ASCII text. The notice should
contain the characters (C), the year of the copyright, and the owner of
the copyright. If several pieces of music are in the same MIDI file,
all of the copyright notices should be placed together in this event so
that it will be at the beginning of the file. This event should be the
first event in the first track block, at time 0.
FF 03 len text Sequence/Track Name
If in a format 0 track, or the first track in a format 1 file, the name
of the sequence. Otherwise, the name of the track.
FF 04 len text Instrument Name
A description of the type of instrumentation to be used in that track.
FF 05 len text Lyric
A lyric to be sung. Generally, each syllable will be a separate lyric
event which begins at the event's time.
FF 06 len text Marker
Normally in a format 0 track, or the first track in a format 1 file.
The name of that point in the sequence, such as a rehearsal letter or
section name ("First Verse", etc.).
FF 07 len text Cue Point
A description of something happening on a film or video screen or stage
at that point in the musical score ("Car crashes into house", "curtain
opens", "she slaps his face", etc.)
FF 2F 00 End of Track
This event is not optional. It is included so that an exact ending
point may be specified for the track, so that it has an exact length,
which is necessary for tracks which are looped or concatenated.
FF 51 03 tttttt Set Tempo, in microseconds per MIDI quarter-note
This event indicates a tempo change. Another way of putting
"microseconds per quarter-note" is "24ths of a microsecond per MIDI
clock". Representing tempos as time per beat instead of beat per time
allows absolutely exact dword-term synchronization with a time-based sync
protocol such as SMPTE time code or MIDI time code. This amount of
accuracy provided by this tempo resolution allows a four-minute piece at
120 beats per minute to be accurate within 500 usec at the end of the
piece. Ideally, these events should only occur where MIDI clocks would
be located Q this convention is intended to guarantee, or at least
increase the likelihood, of compatibility with other synchronization
devices so that a time signature/tempo map stored in this format may
easily be transferred to another device.
FF 54 05 hr mn se fr ff SMPTE Offset
This event, if present, designates the SMPTE time at which the track
block is supposed to start. It should be present at the beginning of
the track, that is, before any nonzero delta-times, and before any
transmittable MIDI events. The hour must be encoded with the SMPTE
format, just as it is in MIDI Time Code. In a format 1 file, the SMPTE
Offset must be stored with the tempo map, and has no meaning in any of
the other tracks. The ff field contains fractional frames, in 100ths of
a frame, even in SMPTE-based tracks which specify a different frame
subdivision for delta-times.
FF 58 04 nn dd cc bb Time Signature
The time signature is expressed as four numbers. nn and dd represent
the numerator and denominator of the time signature as it would be
notated. The denominator is a negative power of two: 2 represents a
quarter-note, 3 represents an eighth-note, etc. The cc parameter
expresses the number of MIDI clocks in a metronome click. The bb
parameter expresses the number of notated 32nd-notes in a MIDI quarter-
note (24 MIDI Clocks).
FF 59 02 sf mi Key Signature
sf = -7: 7 flats
sf = -1: 1 flat
sf = 0: key of C
sf = 1: 1 sharp
sf = 7: 7 sharps
mi = 0: major key
mi = 1: minor key
FF 7F len data Sequencer-Specific Meta-Event
Special requirements for particular sequencers may use this
event type: the first byte or bytes of data is a manufacturer ID.
However, as this is an interchange format, growth of the spec proper is
preferred to use of this event type. This type of event may be used by
a sequencer which elects to use this as its only file format;
sequencers with their established feature-specific formats should
probably stick to the standard features when using this format.
The system exclusive event is used as an escape to specify arbitrary bytes
to be transmitted. The system exclusive event has two forms, to compensate
for some manufacturer-specific modes, the F7h event is used if a F0h is to
be transmitted. Each system exclusive event must end with an F7h event.
The format of a system exclusive event :
OFFSET Count TYPE Description
0000h 1 byte ID=F0h,ID=F7h
0001h ? ? Length as variable length qty.
? byte bytes to be transmitted
EXTENSION:MID,MIDI
OCCURENCES:PC,MAC
PROGRAMS:Cubase
VALIDATION:
International Midi Association
5316 West 57th Street
Los Angeles, CA 90056
xx1-213-649-6434
xx1-213-215-3380 fax
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