Standard MIDI-File Format Spec. 1.1

------------------------------------------ Distributed by: The International MIDI Association 5316 W. 57th St. Los Angeles, CA 90056 (213) 649-6434 0 - Introduction The document outlines the specification for MIDI Files. The purpose of MIDI Files is to provide a way of interchanging time-stamped MIDI data between different programs on the same or different computers. One of the primary design goals is compact representation, which makes it very appropriate for disk-based file format, but which might make it inappropriate for storing in memory for quick access by a sequencer program. (It can be easily converted to a quickly-accessible format on the fly as files are read in or written out.) It is not intended to replace the normal file format of any program, though it could be used for this purpose if desired. 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. This spec defines the 8-bit binary data stream used in the file. The data can be stored in a binary file, nibbilized, 7-bit-ized for efficient MIDI transmission, converted to Hex ASCII, or translated symbolically to a printable text file. This spec addresses what's in the 8-bit stream. It does not address how a MIDI File will be transmitted over MIDI. It is the general feeling that a MIDI transmission protocol will be developed for files in general and MIDI Files will use this scheme. 1 - Sequences, Tracks, Chunks: File Block Structure CONVENTIONS In this document, bit 0 means the least significant bit of a byte, and bit 7 is the most significant. 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
MTrk MTrk . . . 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:
= As described above, is the four ASCII characters 'MThd'; 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, , specifies the overall organization of the file. Only three values of 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, , is the number of track chunks in the file. It will always be 1 for a format 0 file. The third word, , 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 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 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): = + The syntax of an MTrk event is very simple: = 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. = | | 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. 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 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 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. specifies non-MIDI information useful to this format or to sequencers, with this syntax: FF 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