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Standard MIDI-File Format Spec. 1.1
1 - Sequences, Tracks, Chunks: File Block Structure
CONVENTIONS
Some numbers in MIDI Files are represented is a form called 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.
Here are some examples of numbers represented as variable-length
quantities:
00000000 00
00000040 40
0000007F 7F
00000080 81 00
00002000 C0 00
00003FFF FF 7F
00004000 81 80 00
00100000 C0 80 00
001FFFFF FF FF 7F
00200000 81 80 80 00
08000000 C0 80 80 00
0FFFFFFF FF FF FF 7F
The largest number which is allowed is 0FFFFFFF so that the variable-length
representations must fit in 32 bits in a routine to write variable-length
numbers. Theoretically, larger numbers are possible, but 2 x 10^8 96ths of
a beat at a fast tempo of 500 beats per minute is four days, long enough
for any delta-time!
FILES
To any file system, a MIDI File is simply a series of 8-bit bytes. On the
Macintosh, this byte stream is stored in the data fork of a file (with file
type 'MIDI'), or on the Clipboard (with data type 'MIDI'). Most other
computers store 8-bit byte streams in files -- naming or storage
conventions for those computers will be defined as required.
CHUNKS
MIDI Files are made up of -chunks-. Each chunk has a 4-character type and a
32-bit length, which is the number of bytes in the chunk. This structure
allows future chunk types to be designed which may be easily be ignored if
encountered by a program written before teh chunk type is introduced. Your
programs should EXPECT alien chunks and treat them as if they weren't
there.
Each chunk begins with a 4-character ASCII type. It is followed by a 32-bit
length, most significant byte first (a length of 6 is stored as 00 00 00
06). This length refers to the number of bytes of data which follow: the
eight bytes of type and length are not included. Therefore, a chunk with a
length of 6 would actually occupy 14 bytes in the disk file.
This chunk architecture is similar to that used by Electronic Arts' IFF
format, and the chunks described herin could easily be placed in an IFF
file. The MIDI File itself is not an IFF file: it contains no nested
chunks, and chunks are not constrained to be an even number of bytes long.
Converting it to an IFF file is as easy as padding odd length chunks, and
sticking the whole thing inside a FORM chunk.
MIDI Files contain two types of chunks: header chunks and track chunks. A
-header- chunk provides a minimal amount of information pertaining to the
entire MIDI file. A -track- chunk contains a sequential stream of MIDI data
which may contain information for up to 16 MIDI channels. The concepts of
multiple tracks, multiple MIDI outputs, patterns, sequences, and songs may
all be implemented using several track chunks.
A MIDI File always starts with a header chunk, and is followed by one or
more track chunks.
MThd <length of header data>
<header data>
MTrk <length of track data>
<track data>
MTrk <length of track data>
<track data>
. . .
2 - Chunk Descriptions
HEADER CHUNKS
The header chunk at the beginning of the file specifies some basic
information about the data in the file. Here's the syntax of the complete
chunk:
<Header Chunk> = <chunk type><length><format><ntrks><division>
As described above, <chunk type> is the four ASCII characters 'MThd';
<length> is a 32-bit representation of the number 6 (high byte first).
The data section contains three 16-bit words, stored most-significant byte
first.
The first word, <format>, specifies the overall organization of the file.
Only three values of <format> are specified:
0-the file contains a single multi-channel track
1-the file contains one or more simultanious tracks (or MIDI outputs) of a
sequence
2-the file contains one or more sequentially independant single-track
patterns
More information about these formats is provided below.
The next word, <ntrks>, is the number of track chunks in the file. It will
always be 1 for a format 0 file.
The third word, <division>, specifies the meaning of the delta-times. It
has two formats, one for metrical time, and one for time-code-based time:
+---+-----------------------------------------+
| 0 | ticks per quarter-note |
==============================================|
| 1 | negative SMPTE format | ticks per frame |
+---+-----------------------+-----------------+
|15 |14 8 |7 0 |
If bit 15 of <division> is zero, the bits 14 thru 0 represent the number of
delta time "ticks" which make up a quarter-note. For instance, if division
is 96, then a time interval of an eighth-note between two events in the
file would be 48.
If bit 15 of <division> is a one, delta times in a file correspond to
subdivisions of a second, in a way consistent with SMPTE and MIDI Time
Code. Bits 14 thru 8 contain one of the four values -24, -25, -29, or -30,
corresponding to the four standard SMPTE and MIDI Time Code formats (-29
corresponds to 30 drop frome), and represents the number of frames per
second. These negative numbers are stored in two's compliment form. The
second byte (stored positive) is the resolution within a frame: typical
values may be 4 (MIDI Time Code resolution), 8, 10, 80 (bit resolution), or
100. This stream allows exact specifications of time-code-based tracks, but
also allows milisecond-based tracks by specifying 25|frames/sec and a
resolution of 40 units per frame. If the events in a file are stored with a
bit resolution of thirty-framel time code, the division word would be E250
hex.
FORMATS 0, 1, AND 2
A Format 0 file has a header chunk followed by one track chunk. It is the
most interchangable representation of data. It is very useful for a simple
single-track player in a program which needs to make synthesizers make
sounds, but which is primarily concerened with something else such as
mixers or sound effect boxes. It is very desirable to be able to produce
such a format, even if your program is track-based, in order to work with
these simple programs. On the other hand, perhaps someone will write a
format conversion from format 1 to format 0 which might be so easy to use
in some setting that it would save you the trouble of putting it into your
program.
A Format 1 or 2 file has a header chunk followed by one or more track
chunks. programs which support several simultanious tracks should be able
to save and read data in format 1, a vertically one-dementional form, that
is, as a collection of tracks. Programs which support several independant
patterns should be able to save and read data in format 2, a horizontally
one-dementional form. Providing these minimum capabilities will ensure
maximum interchangability.
In a MIDI system with a computer and a SMPTE synchronizer which uses Song
Pointer and Timing Clock, tempo maps (which describe the tempo throughout
the track, and may also include time signature information, so that the bar
number may be derived) are generally created on the computer. To use them
with the synchronizer, it is necessary to transfer them from the computer.
To make it easy for the synchronizer to extract this data from a MIDI File,
tempo information should always be stored in the first MTrk chunk. For a
format 0 file, the tempo will be scattered through the track and the tempo
map reader should ignore the intervening events; for a format 1 file, the
tempo map must be stored as the first track. It is polite to a tempo map
reader to offerr your user the ability to make a format 0 file with just
the tempo, unless you can use format 1.
All MIDI Files should specify tempo and time signature. If they donn't, the
time signature is assumed to be 4/4, and the tempo 120 beats per minute. In
format 0, these meta-events should occur at least at the beginning of the
single multi-channel track. In format 1, these meta-events should be
contained i| the first track. In format 2, each of the temporally
independant patterns should contain at least initial time signature and
tempo information.
We may decide to define other format IDs to support other structures. A
program encountering an unknown format ID may still read other MTrk chunks
it finds from the file, as format 1 or 2, if its user can make sense of
them and arrange them into some other structure if appropriate. Also, more
parameters may be added to the MThd chunk in the future: it is important to
read and honor the length, even if it is longer than 6.
TRACK CHUNKS
The track chunks (type MTrk) are where actual song data is stored. Each
track chunk is simply a stream of MIDI events (and non-MIDI events),
preceded by delta-time values. The format for Track Chunks (described
below) is exactly the same for all three formats (0, 1, and 2: see "Header
Chunk" above) of MIDI Files.
Here is the syntax of an MTrk chunk (the + means "one or more": at least
one MTrk event must be present):
<Track Chunk> = <chunk type><length><MTrk event>+
The syntax of an MTrk event is very simple:
<MTrk event> = <delta-time><event>
<delta-time> is stored as a variable-length quantity. It represents the
amount of time before the following event. If the first event in a track
occurs at the very beginning of a track, or if two events occur
simultaineously, a delta-time of zero is used. Delta-times are always
present. (Not storing delta-times of 0 requires at least two bytes for any
other value, and most delta-times aren't zero.) Delta-time is in some
fraction of a beat (or a second, for recording a track with SMPTE times),
as specified in the header chunk.
<event> = <MIDI event> | <sysex event> | <meta-event>
<MIDI event> is any MIDI channel message. Running status is used: status
bytes of MIDI channel messages may be omitted if the preceding event is a
MIDI channel message with the same status. The first event in each MTrk
chunk must specifyy status. Delta-time is not considered an event itself:
it is an integral part of the syntax for an MTrk event. Notice that running
status occurs across delta-times.
<sysex event> is used to specify a MIDI system exclusive message, either as
one unit or in packets, or as an "escape" to specify any arbitrary bytes to
be transmitted. A normal complete system exclusive message is stored in a
MIDI File in this way:
F0 <length> <bytes to be transmitted after F0>
The length is stored as a variable-length quantity. It specifies the number
of bytes which follow it, not including the F0 or the length itself. For
instance, the transmitted message F0 43 12 00 07 F7 would be stored in a
MIDI File as F0 05 43 12 00 07 F7. It is required to include the F7 at the
end so that the reader of the MIDI File knows that it has read the entire
message.
Another form of sysex event is provided which does not imply that an F0
should be transmitted. This may be used as an "escape" to provide for the
transmission of things which would not otherwise be legal, including system
realtime messages, song pointer or select, MIDI Time Code, etc. This uses
the F7 code:
F7 <length> <all bytes to be transmitted>
Unfortunately, some synthesizer manufacturers specify that their system
exclusive messages are to be transmitted as little packets. Each packet is
only part of an entire syntactical system exclusive message, but the times
they are transmitted are important. Examples of this are the bytes sent in
a CZ patch dump, or the FB-01's "system exclusive mode" in which microtonal
data can be transmitted. The F0 and F7 sysex events may be used together to
break up syntactically complete system exclusive messages into timed
packets.
An F0 sysex event is used for the first packet in a series -- it is a
message in which the F0 should be transmitted. An F7 sysex event is used
for the remainder of the packets, which do not begin with F0. (Of course,
the F7 is not considered part of the system exclusive message).
A syntactic system exclusive message must always end with an F7, even if
the real-life device didn't send one, so that you know when you've reached
the end of an entire sysex message without looking ahead to the next event
in the MIDI File. If it's stored in one compllete F0 sysex event, the last
byte must be an F7. There also must not be any transmittable MIDI events in
between the packets of a multi-packet system exclusive message. This
principle is illustrated in the paragraph below.
Here is a MIDI File of a multi-packet system exclusive message: suppose the
bytes F0 43 12 00 were to be sent, followed by a 200-tick delay, followed
by the bytes 43 12 00 43 12 00, followed by a 100-tick delay, followed by
the bytes 43 12 00 F7, this would be in the MIDI File:
F0 03 43 12 00
81 48 200-tick delta time
F7 06 43 12 00 43 12 00
64 100-tick delta time
F7 04 43 12 00 F7
When reading a MIDI File, and an F7 sysex event is encountered without a
preceding F0 sysex event to start a multi-packet system exclusive message
sequence, it should be presumed that the F7 event is being used as an
"escape". In this case, it is not necessary that it end with an F7, unless
it is desired that the F7 be transmitted.
<meta-event> specifies non-MIDI information useful to this format or to
sequencers, with this syntax:
FF <type> <length> <bytes>
All meta-events begin with FF, then have an event type byte (which is
always less than 128), and then have the length of the data stored as a
variable-length quantity, and then the data itself. If there is no data,
the length is 0. As with chunks, future meta-events may be designed which
may not be known to existing programs, so programs must properly ignore
meta-events which they do not recognize, and indeed should expect to see
them. Programs must never ignore the length of a meta-event which they do
not recognize, and they shouldn't be surprized if it's bigger than
expected. If so, they must ignore everything past what they know about.
However, they must not add anything of their own to the end of the meta-
event.
Sysex events and meta events cancel any running status which was in effect.
Running status does not apply to and may not be used for these messages.
3 - Meta-Events
A few meta-events are defined herin. It is not required for every program
to support every meta-event.
In the syntax descriptions for each of the meta-events a set of conventions
is used to describe parameters of the events. The FF which begins each
event, the type of each event, and the lengths of events which do not have
a variable amount of data are given directly in hexadecimal. A notation
such as dd or se, which consists of two lower-case letters, mnemonically
represents an 8-bit value. Four identical lower-case letters such as wwww
mnemonically refer to a 16-bit value, stored most-significant-byte first.
Six identical lower-case letters such as tttttt refer to a 24-bit value,
stored most-significan-byte first. The notation len refers to teh length
portion of the meta-event syntax, that is, a number, stored as a variable-
length quantity, which specifies how many bytes (possibly text) data were
just specified by the length.
In general, meta-events in a track which occur at the same time may occur
in any order. If a copyright event is used, it should be placed as early as
possible in the file, so it will be noticed easily. Sequence Number and
Sequence/Track Name events, if present, must appear at time 0. An end-of-
track event must occur as the last event in the track.
Meta-events initially defined include:
FF 00 02 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. In a format 2 MIDI File, it
is used to identify each "pattern" so that a "song" sequence using the
Cue message to refer to the patterns. If the ID numbers are omitted,
the sequences' lacations in order in the file are used as defaults. In
a format 0 or 1 MIDI File, which only contain one sequence, this number
should be contained in the first (or only) track. If transfer of
several multitrack sequences is required, this must be done as a group
of format 1 files, each with a different sequence number.
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. Text events may also occur at other
times in a track, to be used as lyrics, or descriptions of cue points.
The text in this event should be printable ASCII characters for maximum
interchange. However, other characters codes using the high-order bit
may be used for interchange of files between different programs on the
same computer which supports an extended character set. Programs on a
computer which does not support non-ASCII characters should ignore
those characters.
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 track chunk, 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.
May be used with the MIDI Prefix meta-event to specify which MIDI
channel the description applies to, or the channel may be specified as
text in the event itself.
FF 05 len text Lyric
A lyric to be sung. Generally, each syllable will be a seperate 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 rehersal 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 20 01 cc MIDI Channeel Prefix
The MIDI channel (0-15) containted in this event may be used to
associate a MIDI channel with all events which follow, including System
exclusive and meta-events. This channel is "effective" until the next
normal MIDI event (which contains a channel) or the next MIDI Channel
Prefix meta-event. If MIDI channels refer to "tracks", this message may
into a format 0 file, keeping their non-MIDI data associated with a
track. This capability is also present in Yamaha's ESEQ file format.
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 an exect 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". Repersenting tempos as time per beat instead of beat per time
allows absolutly exact long-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 -- this convention is intended to guarntee, or at
least increase the liklihood, of compatibility with other
synchronization devices so that a time signature/tempo map stored in
this format may easily be transfered 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
chunk 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 neqative 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). This was added because there are already
multiple programs which allow a user to specify that what MIDI thinks
of as a quarter-note (24 clocks) is to be notated as, or related to in
terms of, something else.
Therefore, the complete event for 6/8 time, where the metronome clicks
every three eighth-notes, but there are 24 clocks per quarter-note, 72
to the bar, would be (in hex):
FF 58 04 06 03 24 08
That is, 6/8 time (8 is 2 to the 3rd power, so this is 06 03), 36 MIDI
clocks per dotted-quarter (24 hex!), and eight notated 32nd-notes per
quarter-note.
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 (these are one
byte, or if the first byte is 00, three bytes). As with MIDI System
Exclusive, manufacturers who define something using this meta-event
should publish it so that others 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.
4 - Program Fragments and Example MIDI Files
Here are some of the routines to read and write variable-length numbers in
MIDI Files. These routines are in C, and use getc and putc, which read and
write single 8-bit characters from/to the files infile and outfile.
WriteVarLen (value)
register long value;
(
register long buffer;
buffer = value & 0x7f;
while ((value >>= 7) > 0)
(
buffer <<= 8;
buffer |= 0x80;
buffer += (value & 0x7f);
)
while (TRUE)
(
putc(buffer,outfile);
if (buffer & 0x80)
buffer >>= 8;
else
break;
)
)
doubleword ReadVarLen ()
(
register doubleword value;
register byte c;
if ((value = getc(infile)) & 0x80)
(
value &= 0x7f;
do
(
value = (value << 7) + ((c = getc(infile))) & 0x7f);
) while (c & 0x80);
)
return (value);
)
As an example, MIDI Files for the following excerpt are shown below. First,
a format 0 file is shown, with all information intermingled; then, a format
1 file is shown with all data seperated into four tracks: one for tempo and
time signature, and three for the notes. A resolution of 96 "ticks" per
quarter note is used. A time signature of 4/4 and a tempo of 120, though
implied, are explicitly stated.
|\
---- | > ---------------------------------------
|/ ____ O
Channel 1 ---- X --------------------------------|--------
/ |
Preset 5 -- / | --------------------------------|--------
/ ____ |
-| | \ --------------------------------------
\ | |
-- \_|__/ --------------------------------------
_|
|\
---- | > ---------------------------------------
|/ \
Channel 2 ---- X ------------>----------|-----------------
/ / |
Preset 46 -- / | ----------<------------|-----------------
/ ____ \ | .
-| | \ --------->---------O------------------
\ | | (
-- \_|__/ --------\-----------------------------
_| \
--O--
----__ -----------------------------------------
/ \ .
Channel 3 - / | ---------------------------------------
| .
Preset 70 ------ | ---------------------------------------
/ O
---- / -----------------------------------------
/
-- / -------------------------------------------
The contents of the MIDI stream represented by this example are broken down
here:
Delta-Time Event-Code Other Bytes Comment
(decimal) (hex) (decimal)
---------- ---------- ----------- -----------------------------
0 FF 58 04 04 02 24 08 4 bytes; 4/4 time; 24 MIDI
clocks/click, 8 32nd notes/
24 MIDI clocks
0 FF 51 03 500000 3 bytes: 500,000 usec/
quarter note
0 C0 5 Ch.1 Program Change 5
0 C1 46 Ch.2 Program Change 46
0 C2 70 Ch.3 Program Change 70
0 92 48 96 Ch.3 Note On C2, forte
0 92 60 96 Ch.3 Note On C3, forte
96 91 67 64 Ch.2 Note On G3, mezzo-forte
96 90 76 32 Ch.1 Note On E4, piano
192 82 48 64 Ch.3 Note Off C2, standard
0 82 60 64 Ch.3 Note Off C3, standard
0 81 67 64 Ch.2 Note Off G3, standard
0 80 76 64 Ch.1 Note Off E4, standard
0 FF 2F 00 Track End
The entire format 0 MIDI file contents in hex follow. First, the header
chunk:
40 54 68 64 MThd
00 00 00 06 chunk length
00 00 format 0
00 01 one track
00 60 96 per quarter-note
Then the track chunk. Its header followed by the events (notice the running
status is used in places):
4D 54 72 6B MTrk
00 00 00 3B chunk length (59)
Delta-Time Event Comments
---------- ----------------------- -------------------------------
00 FF 58 04 04 02 18 08 time signature
00 FF 51 03 07 A1 20 tempo
00 C0 05
00 C1 2E
00 C2 46
00 92 30 60
00 3C 60 running status
60 91 43 40
60 90 4C 20
81 40 82 30 40 two-byte delta-time
00 3C 40 running status
00 81 43 40
00 80 4C 40
00 FF 2F 00 end of track
A format 1 representation of the file is slightly different. Its header
chunk:
4D 54 68 64 MThd
00 00 00 06 chunk length
00 01 format 1
00 04 four tracks
00 60 96 per quarter note
First, the track chunk for the time signature/tempo track. Its header,
followed by the events:
4D 54 72 6B MTrk
00 00 00 14 chunk length (20)
Delta-Time Event Comments
---------- ----------------------- -------------------------------
00 FF 58 04 04 02 18 08 time signature
00 FF 51 03 07 A1 20 tempo
83 00 FF 2F 00 end of track
Then, the track chunk for the first music track. The MIDI convention for
note on/off running status is used in this example:
4D 54 72 6B MTrk
00 00 00 10 chunk length (16)
Delta-Time Event Comments
---------- ----------------------- -------------------------------
00 C0 05
81 40 90 4C 20
81 40 4C 00 Running status: note on, vel=0
00 FF 2F 00
Then, the track chunk for the second music track:
4D 54 72 6B MTrk
00 00 00 0F chunk length (15)
Delta-Time Event Comments
---------- ----------------------- -------------------------------
00 C1 2E
60 91 43 40
82 20 43 00 running status
00 FF 2F 00 end of track
Then, the track chunk for the third music track:
4D 54 72 6B MTrk
00 00 00 15 chunk length (21)
Delta-Time Event Comments
---------- ----------------------- -------------------------------
00 C2 46
00 92 30 60
00 3C 60 running status
83 00 30 00 two-byte delta-time, running status
00 3C 00 running status
00 FF 2F 00 end of track