MIDI Assoc., 01-09-94
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
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