Midi File Format

Reference: Sonicspot

Data Formats

All data values are stored in Big-Endian (most significant byte first) format. And there are variable-length values, which use the lower 7 bits of a byte for data and the top bit to signal a following data byte. If the top bit is set to 1, then another value byte follows. Below is a table of examples to help demonstrate how variable length values are used. For example, the values could be

0x00, 00000000
0xC8, 11001000
0x100000, 00010000 00000000 00000000

and the variable-length values could be

0x00, **0**0000000
0x8148, **1**0000001 **0**1001000
0xC08000, **1**1000000 **1**0000000 **0**0000000

A variable-length value may use a maximum of 4 bytes. This means the maximum value that can be represented is 0x0FFFFFFF (represented as 0xFF, 0xFF, 0xFF, 0x7F).

File Structure

MIDI files are organized into data chunks (similar to RIFF files). Each chunk is prefixed with an 8 byte header: 4 byte ID string used to identify the type of chunk followed by a 4 byte size which defines the chunk's length as number of bytes following this chunk's header.

Header Chunk

Offset	Length	Type	Description	Value
0x00	4	char[4]	chunk ID	"MThd" (0x4D546864)
0x04	4	dword	chunk size	6 (0x00000006)
0x08	2	word	format type	0, 1, 2
0x10	2	word	number of tracks	1 - 65,535
0x12	2	word	time division	see following text

Format Type

0: Single Trace

1: Synchronized Multi Traces

2: Asynchronized Multi Traces

Time Division

The Time Division is 16 bits long, as the first bit is used to stand for method, the following 15 bits are to describe the value.

Top Bit	Following
0	the following 15 bits describe the time division in ticks per beat. Ticks per beat translate to the number of clock ticks or track delta positions (described in the Track Chunk section) in every quarter note of music. Common values range from 48 to 960, although newer sequencers go far beyond this range to ease working with MIDI and digital audio together.
1	the following 15 bits (bit mask 0x7FFF) describe the time division in frames per second. Frames per second is defined by breaking the remaining 15 bytes into two values:[7][1][7]. The top 7 bits (bit mask 0x7F00) define a value for the number of SMPTE frames and can be 24, 25, 29 (for 29.97 fps) or 30. The remaining byte (bit mask 0x00FF) defines how many clock ticks or track delta positions there are per frame. So a time division example of 0x9978 could be broken down into it's three parts: the top bit is one, so it is in SMPTE frames per second format, the following 7 bits have a value of 25 (0x19) and the bottom byte has a value of 120 (0x78). This means the example plays at 24 frames per second SMPTE time and has 120 ticks per frame.

Track Chunk

Offset	Length	Type	Description	Value
0x00	4	char[4]	chunk ID	"MTrk" (0x4D54726B)
0x04	4	dword	chunk size	see following text
0x08			track event data (see following text)

Chunk ID and Size

The chunk ID is always "MTrk" (0x4D54726B) and the size varies depending on the number of bytes used for all of the events
contained in the track.

Track Event Data

The track event data contains a stream of MIDI events that define information about the sequence and how it is played. The next section describes the different types of events.

MIDI Events

Track events are used to describe all of the musical content of a MIDI file, from tempo changes to sequence and track titles to individual music events. Each event includes a delta time, event type and usually some event type specific data.

Delta-Times

The event delta time is defined by a variable-length value. It determines when an event should be played relative to the track's last event.

A delta time of 0 means that it should play simultaneously with the last event. A track's first event delta time defines the amount of time to wait before playing this first event. Events unaffected by time are still preceded by a delta time, but should always use a value of 0 and come first in the stream of track events. Examples of this type of event include track titles and copyright information.

The most important thing to remember about delta times is that they are relative values, not absolute times. The actual time they represent is determined by a couple factors. The time division (defined in the MIDI header chunk) and the tempo (defined with a track event). If no tempo is define, 120 beats per minute is assumed.

Types of Events

There are three types of events: MIDI Control Events, System Exclusive Events and Meta Events.

MIDI Channel Events

Delta Time| Event Type Value| MIDI Channel| Parameter 1| Parameter 2
---|----|----|----
variable-length| 4 bits| 4 bits| 1 byte| 1 byte

The Common Event Types

Event Type	Value	Channel	Parameter 1	Parameter 2
Note Off	0x8	0-15	note number(0-127)	velocity(0-127)
Note On	0x9	0-15	note number(0-127)	velocity(0-127)
Note Aftertouch	0xA	0-15	note number(0-127)	aftertouch value(0-127)
Controller	0xB	0-15	controller number(0-127)	controller value(0-127)
Program Change	0xC	0-15	program number(0-127)	not used
Channel Aftertouch	0xD	0-15	aftertouch value(0-127)	not used
Pitch Bend	0xE	0-15	pitch value (LSB)(0-127)	pitch value (MSB)(0-127)

Note Off

Key Released

Note On

Key Pressed

Note Aftertouch

The Note Aftertouch Event is used to indicate a pressure change on one of the currently pressed MIDI keys. The aftertouch value which specifies amount of pressure being applied (0 = no pressure, 127 = full pressure). Note Aftertouch is used for extra expression of particular notes, often introducing or increasing some type of modulation during the instrument's sustain phase.

Controller Event

The Controller Event signals the change in a MIDI channels state. There are 128 controllers which define different attributes of the channel including volume, pan, modulation, effects, and more. This event type has two parameters. The controller number specifies which control is changing and the controller value defines it's new setting.

Value	Controller Type
0 (0x00)	Bank Select
1 (0x01)	Modulation
2 (0x02)	Breath Controller
4 (0x04)	Foot Controller
5 (0x05)	Portamento Time
6 (0x06)	Data Entry (MSB)
7 (0x07)	Main Volume
8 (0x08)	Balance
10 (0x0A)	Pan
11 (0x0B)	Expression Controller
12 (0x0C)	Effect Control 1
13 (0x0D)	Effect Control 2
16-19 (0x10-0x13)	General-Purpose Controllers 1-4
32-63 (0x20-0x3F)	LSB for controllers 0-31
64 (0x40)	Damper pedal (sustain)
65 (0x41)	Portamento
66 (0x42)	Sostenuto
67 (0x43)	Soft Pedal
68 (0x44)	Legato Footswitch
69 (0x45)	Hold 2
70 (0x46)	Sound Controller 1 (default: Timber Variation)
71 (0x47)	Sound Controller 2 (default: Timber/Harmonic Content)
72 (0x48)	Sound Controller 3 (default: Release Time)
73 (0x49)	Sound Controller 4 (default: Attack Time)
74-79 (0x4A-0x4F)	Sound Controller 6-10
80-83 (0x50-0x53)	General-Purpose Controllers 5-8
84 (0x54)	Portamento Control
91 (0x5B)	Effects 1 Depth (formerly External Effects Depth)
92 (0x5C)	Effects 2 Depth (formerly Tremolo Depth)
93 (0x5D)	Effects 3 Depth (formerly Chorus Depth)
94 (0x5E)	Effects 4 Depth (formerly Celeste Detune)
95 (0x5F)	Effects 5 Depth (formerly Phaser Depth)
96 (0x60)	Data Increment
97 (0x61)	Data Decrement
98 (0x62)	Non-Registered Parameter Number (LSB)
99 (0x63)	Non-Registered Parameter Number (MSB)
100 (0x64)	Registered Parameter Number (LSB)
101 (0x65)	Registered Parameter Number (MSB)
121-127 (0x79-0x7F)	Mode Messages

Program Change Event

The Program Change Event is used to change which program (instrument/patch) should be played on the MIDI channel. This type of event takes only one parameter, the program number of the new instrument/patch.

Channel Aftertouch Event

The Channel Aftertouch Event is similar to the Note Aftertouch message, except it effects all keys currently pressed on the specific MIDI channel. This type of event takes only one parameter, the aftertouch amount (0 = no pressure, 127 = full pressure).

Pitch Bend Event

The Pitch Bend Event is similar to a controller event, except that it is a unique MIDI Channel Event that has two bytes to describe it's value. The pitch value is defined by both parameters of the MIDI Channel Event by joining them in the format of yyyyyyyxxxxxxx where the y characters represent the last 7 bits of the second parameter and the x characters represent the last 7 bits of the first parameter. The combining of both parameters enables high accuracy values (0 - 16383). The pitch value affects all playing notes on the current channel. Values below 8192 decrease the pitch, while values above 8192 increase the pitch. The pitch range may vary from instrument to instrument, but is usually +/-2 semi-tones.

Meta Events

Events that are not to be sent or received over a MIDI port are called Meta Events. These events are defined by an event type value of 0xFF and have a variable size of parameter data which is defined after the event type.

Meta Event| Type| Length| Data
255 (0xFF)| 0-255| variable-length| type specific

Sequence Number

This meta event defines the pattern number of a Type 2 MIDI file or the number of a sequence in a Type 0 or Type 1 MIDI file. This meta event should always have a delta time of 0 and come before all MIDI Channel Events and non-zero delta time events.

Meta Event	Type	Length	Number (MSB)	Number (LSB)
255 (0xFF)	0 (0x00)	2	0-255	0-255

Text Event

This meta event defines some text which can be used for any reason including track notes, comments, etc. The text string is usually ASCII text, but may be any character (0x00-0xFF).

Meta Event	Type	Length	Text
255 (0xFF)	1 (0x01)	string length	ASCII text

Copyright Notice

This meta event defines copyright information including the copyright symbol © (0xA9), the year and the author. This meta event should always be in the first track chunk, have a delta time of 0 and come before all MIDI Channel Events and non-zero delta time events.

Meta Event	Type	Length	Text
255 (0xFF)	2 (0x02)	string length	ASCII text

Sequence/Track Name

This meta event defines the name of a sequence when in a Type 0 or Type 2 MIDI file or in the first track of a Type 1 MIDI file. It defines a track name when it appears in any track after the first in a Type 1 MIDI file. This meta event should always have a delta time of 0 and come before all MIDI Channel Events and non-zero delta time events.

Meta Event	Type	Length	Text
255 (0xFF)	3 (0x03)	string length	ASCII text

Instrument Name

This meta event defines the name of an instrument being used in the current track chunk. This event can be used with the MIDI Channel Prefix meta event to define which instrument is being used on a specific channel.

Meta Event	Type	Length	Text
255 (0xFF)	4 (0x04)	string length	ASCII text

Lyrics

This meta event defines the lyrics in a song and are usually used to define a syllable or group of works per quarter note. This event can be used as an equivalent of sheet music lyrics or for implementing a karaoke-style system.

Meta Event	Type	Length	Text
255 (0xFF)	5 (0x05)	string length	ASCII text

Marker

This meta event marks a significant point in time for the sequence. It is usually found in the first track chunk, but may appear in any one. This event can be useful for marking the beginning/end of a new verse or chorus.

Meta Event	Type	Length	Text
255 (0xFF)	6 (0x06)	string length	ASCII text

Cue Point

This meta event marks the start of some type of new sound or action. It is usually found in the first track chunk, but may appear in any one. This event is sometimes used by sequencers to mark when playback of a sample or video should begin.

Meta Event	Type	Length	Text
255 (0xFF)	7 (0x07)	string length	ASCII text

MIDI Channel Prefix

This meta event associates a MIDI channel with following meta events. It's effect is terminated by another MIDI Channel Prefix event or any non- Meta event. It is often used before an Instrument Name Event to specify which channel an instrument name represents.

Meta Event	Type	Length	Channel
255 (0xFF)	32 (0x20)	1	0-15

End Of Track

This meta event is used to signal the end of a track chunk and must always appear as the last event in every track chunk.

Meta Event| Type| Length
----|----|----|----
255 (0xFF)| 47 (0x2F)| 0

Set Tempo

This meta event sets the sequence tempo in terms of microseconds per quarter-note which is encoded in three bytes. It usually is found in the first track chunk, time-aligned to occur at the same time as a MIDI clock message to promote more accurate synchronization. If no set tempo event is present, 120 beats per minute is assumed. The following formula's can be used to translate the tempo from microseconds per quarter-note to beats per minute and back.

MICROSECONDS_PER_MINUTE = 60000000

BPM = MICROSECONDS_PER_MINUTE / MPQN

MPQN = MICROSECONDS_PER_MINUTE / BPM

Meta Event	Type	Length	Microseconds/Quarter-Note
255 (0xFF)	81 (0x51)	3	0-8355711

SMPTE Offset

This meta event is used to specify the SMPTE starting point offset from the beginning of the track. It is defined in terms of hours, minutes, seconds, frames and sub-frames (always 100 sub-frames per frame, no matter what sub-division is specified in the MIDI header chunk). The byte used to specify the hour offset also specifies the frame rate in the following format: 0rrhhhhhh where rr is two bits for the frame rate where 00=24 fps, 01=25 fps, 10=30 fps (drop frame), 11=30 fps and hhhhhh is six bits for the hour (0-23). The hour byte's top bit is always 0. The frame byte's possible range depends on the encoded frame rate in the hour byte. A 25 fps frame rate means that a maximum value of 24 may be set for the frame byte.

Meta Event| Type| Length| Hour| Min| Sec| Fr| SubFr
----|----|----|----|----|----|----
255 (0xFF)| 84 (0x54)| 5| 0-23 *| 0-59| 0-59| 0-30 *| 0-99

Time Signature

This meta event is used to set a sequences time signature. The time signature defined with 4 bytes, a numerator, a denominator, a metronome pulse and number of 32nd notes per MIDI quarter-note. The numerator is specified as a literal value, but the denominator is specified as (get ready) the value to which the power of 2 must be raised to equal the number of subdivisions per whole note. For example, a value of 0 means a whole note because 2 to the power of 0 is 1 (whole note), a value of 1 means a half-note because 2 to the power of 1 is 2 (half-note), and so on. The metronome pulse specifies how often the metronome should click in terms of the number of clock signals per click, which come at a rate of 24 per quarter-note. For example, a value of 24 would mean to click once every quarter-note (beat) and a value of 48 would mean to click once every half-note (2 beats). And finally, the fourth byte specifies the number of 32nd notes per 24 MIDI clock signals. This value is usually 8 because there are usually 8 32nd notes in a quarter-note. At least one Time Signature Event should appear in the first track chunk (or all track chunks in a Type 2 file) before any non-zero delta time events. If one is not specified 4/4, 24, 8 should be assumed.

Meta Event	Type	Length	Numer	Denom	Metro	32nds
255 (0xFF)	88 (0x58)	4	0-255	0-255	0-255	1-255

Key Signature

This meta event is used to specify the key (number of sharps or flats) and scale (major or minor) of a sequence. A positive value for the key specifies the number of sharps and a negative value specifies the number of flats. A value of 0 for the scale specifies a major key and a value of 1 specifies a minor key.

Meta Event	Type	Length	Key	Scale
255 (0xFF)	89 (0x59)	2	-7-7	0-1

Sequencer Specific

This meta event is used to specify information specific to a hardware or software sequencer. The first Data byte (or three bytes if the first byte is 0) specifies the manufacturer's ID and the following bytes contain information specified by the manufacturer. The individual manufacturers may document this information in their respective manuals.

Meta Event	Type	Length	Data
255 (0xFF)	127 (0x7F)	variable-length	any type and amount *

System Exclusive Events

Also known as SysEx Events, these MIDI events are used to control MIDI hardware or software that require special data bytes that will follow their manufacturer's specifications. Every SysEx event includes an ID that specifies which manufacturer's product is to be the intended receiver. All other products will ignore the event. There are three types of SysEx messages which are used to send data in a single event, across multiple events or authorize the transmission of specific MIDI messages.

Normal SysEx Events

These are the most common type of SysEx event and are used to hold a single block of manufacturer specific data. The first byte is always 0xF0 and the second is a variable-length value that specifies the length of the following SysEx data in bytes. The SysEx data bytes must always end with a 0xF7 byte to signal the end of the message.

SysEx Event	Length	Data
240 (0xF0)	variable-length	data bytes, 0xF7

Divided SysEx Events

A large amount of SysEx data in a Normal SysEx Event could cause following MIDI Channel Events to be transmitted after the time they should be played. This will cause an unwanted delay in play back of the following events. The second type of SysEx Events solve this problem by allowing a large amount of SysEx data to be divided into smaller blocks, transmitted with a delay between each division to allow the transmission of other MIDI events in order to prevent congesting of the limited MIDI bandwidth. The initial Divided SysEx Event follows the same format as a Normal SysEx Event with the exception that the last data byte is not 0xF7. This indicates the the SysEx data is not finished and will be continued in an upcoming Divided SysEx Event. Any following Divided SysEx Events before the final one use the a similar format as the first, only the start byte is 0xF0 instead of 0xF7 to signal continuation of SysEx data. The final block follows the same format as the continuation blocks, except the last data byte is 0xF7 to signal the completion of the divided SysEx data.

SysEx Event	Length	Data
240 (0xF0)	variable-length	data bytes
247 (0xF7)	variable-length	data bytes
247 (0xF7)	variable-length	data bytes, 0xF7

Authorization SysEx Events

The last type of SysEx Event authorizes and enables the transmission of special messages such as Song Position Pointer, MIDI Time Code and Song Select messages. These SysEx Events use the event type value 0xF7.

SysEx Event| Length| Data
247 (0xF7)| variable-length| data bytes