MIDIFILE(3)

NAME
mfread,mfwrite - read and write a standard MIDI file

SYNOPSIS
#include "mfread.h"

mfread ()

int (*Mf_getc) ();
int (*Mf_putc) ();
int (*Mf_error) (char *msg);
int (*Mf_header) (int format, int ntrks, int division);
int (*Mf_trackstart) ();
int (*Mf_trackend) ();
int (*Mf_noteon) (int chan, int pitch, int vol);
int (*Mf_noteoff) (int chan, int pitch, int vol);
int (*Mf_pressure) (int chan, int pitch, int pressure);
int (*Mf_parameter) (int chan, int control, int value);
int (*Mf_pitchbend) (int chan, int msb, int lsb);
int (*Mf_program) (int chan, int program);
int (*Mf_chanpressure) (int chan, int pressure);
int (*Mf_sysex) (int leng, char *msg);
int (*Mf_metamisc) (int type, int leng, int msg);
int (*Mf_seqspecific) (int type, int leng, int msg);
int (*Mf_seqnum) (int num);
int (*Mf_text) (int type, int leng, int msg);
int (*Mf_eot) ();
int (*Mf_timesig) (int numer, int denom, int clocks, int qnotes);
int (*Mf_smpte) (int hour, int min, int sec, int frame, int fract);
int (*Mf_tempo) (int microsecs);
int (*Mf_keysig) (int sharpflat, int minor);
int (*Mf_arbitrary) (int leng, int msg);
int Mf_nomerge;
long Mf_currtime;

mfwrite(int format, int ntracks, int division, FILE *fp)

int (*Mf_writetrack)(int track);
int (*Mf_writetempotrack)();

void mf_write_midi_event(delta, type, chan, data, size)
unsigned long delta;
unsigned int type,chan,size;
char *data;

void mf_write_meta_event(delta, type, data, size)
unsigned long delta;
unsigned int type,chan,size;
char *data;

void mf_write_tempo(tempo)
unsigned long tempo;

unsigned long mf_sec2ticks(float seconds, int division, int tempo)
float seconds;
int division;
unsigned int tempo;

float mf_ticks2sec(ticks, division, tempo)
unsigned long ticks;
int division;
unsigned int tempo;

DESCRIPTION
The mfread function reads and interprets a standard MIDI file. To use it you need to understand the general form of a MIDI file and the type of information it contains, but you don't need to know much, if anything, about the detailed format of the file and the mechanics of reading it reliably and portably.

The mfwrite function writes a standard MIDI file making use of user-defined functions that access the program's data structure. To use it you need to define your own Mf_writetrack routine and then make use of the write_* family of routines to write out the MIDI data. The mfwrite routine takes care of the file format and writing the file and track chunk headers.

READING STANDARD MIDI FILES
A single call to mfread will read an entire MIDI file. The interface to mfread is a set of external variables named Mf_*, most of which are function pointers to be called from within mfread during the process of parsing the MIDI file. Before calling mfread, the only requirement is that you assign a value to Mf_getc - a pointer to a function that will return characters from the MIDI file, using -1 to indicate EOF. All the rest of the function pointers are initialized to NULL, and the default action for each is to do nothing. The following is a complete program using mfread that could serve as a 'syntax checker' for MIDI files:

#include <stdio.h>
#include "midifile.h"

mygetc()
{
	/* use standard input */
	return(getchar());
}

main()
{
	Mf_getc = mygetc;
	mfread();
	exit(0);
}

This takes advantage of the default action when an error is detected, which is to exit silently with a return code of 1. An error function of your own can be used by giving a value to Mf_error; the function will be called with the error message as an argument. The other Mf_* variables can similarly be used to call arbitrary functions while parsing the MIDI file. The descriptions below of the information passed to these functions is sparse; refer to the MIDI file standard for the complete descriptions.

Mf_header is the first function to be called, and its arguments contain information from the MIDI file's header; the format (0,1, or 2), the number of tracks, and the division of a quarter-note that defines the times units. Mf_trackstart and Mf_trackend are called at the beginning and end of each track.

Once inside a track, each separate message causes a function to be called. For example, each note-on message causes Mf_noteon to be called with the channel, pitch, and volume as arguments. The time at which the message occurred is stored in Mf_currtime - one of the few external variables that isn't a function pointer. The other channel messages are handled in a similar and obvious fashion - Mf_noteoff, Mf_pressure, Mf_parameter, Mf_pitchbend, Mf_program, and Mf_chanpressure. See the declarations above for the arguments that are passed to each.

System exclusive messages are handled by calling Mf_sysex, passing as arguments the message length and a pointer to a static buffer containing the entire message. The buffer is expanded when necessary; memory availability is the only limit to its size. Normally, 'continued' system exclusives are automatically merged, and Mf_sysex is only called once. It you want to disable this you can set Mf_nomerge to 1, causing Mf_sysex to be called once for each part of the message.

Mf_seqnum is called by the meta message that provides a sequence number, which if present must appear at the beginning of a track. The tempo meta message causes Mf_tempo to be called; its argument is the number of microseconds per MIDI quarter-note (24 MIDI clocks). The end-of-track meta message causes Mf_eot to be called. The key signature meta message causes Mf_keysig to be called; the first argument conveys the number of sharps or flats, the second argument is 1 if the key is minor.

The Mf_timesig and Mf_smpte functions are called when the corresponding meta messages are seen. See the MIDI file standard for a description of their arguments.

The text messages in the MIDI file standard are of the following types:

0x01		Text Event
0x02		Copyright
0x03		Sequence/Track Name
0x04		Instrument
0x05		Lyric
0x06		Marker
0x07		Cue Point
0x08-0x0F	Reserved but Undefined

Mf_text is called for each of these; the arguments are the type number, the message length, and a pointer to the message buffer.

Miscellaneous meta messages are handled by Mf_metamisc, sequencer-specific messages are handled by Mf_seqspecific, and arbitrary "escape" messages (started with 0xF7) are handled by Mf_arbitrary.

READING EXAMPLE
The following is a strings-like program for MIDI files:

#include <stdio.h>
#include <ctype.h>
#include "midifile.h"

FILE *F;

mygetc() { return(getc(F)); }

mytext(type,leng,msg)
char *msg;
{
	char *p;
	char *ep = msg + leng;

	for ( p=msg; p<ep ; p++ )
		putchar( isprint(*p) ? *p : '?' );
	putchar(');
}

main(argc,argv)
char **argv;
{
	if ( argc > 1 )
		F = fopen(argv[1],"r");
	else
		F = stdin;

	Mf_getc = mygetc;
	Mf_text = mytext;

	mfread();

	exit(0);
}

WRITING STANDARD MIDI FILES
A single call to mfwrite will write an entire MIDI file. Before calling mfwrite, you must assign values to function pointers Mf_writetrack and Mf_putc. The first is a routine to access your MIDI data structure, which can make use of other library routines to write the actual MIDI data. The routine Mf_writetrack will be passed a single parameter which is the number of the track to be written. The pointer Mf_putc should be set to point to a routine that accepts a character as input, writes that character to a file, and returns the value that was written. In the case of a format 1 file, a routine has to be written to write a tempo map, and assigned to the function pointer Mf_writetempotrack. This is because format 1 files assume the first track written is a tempo track.

mf_write_midi_event and mf_write_meta_event are routines that should be called from your Mf_writetrack routine to write out MIDI events. The delta time param is the number of ticks since the last event. The int "type" is the type of MIDI message. The int "chan" is the MIDI channel, which can be between 1 and 16. The char pointer "data" points to an array containing the data bytes, if any exist. The int "size" is the number of data bytes.

mf_sec2ticks and mf_ticks2sec are utility routines to help you convert between the MIDI file parameter of ticks and the more standard seconds. The int "division" is the same division parameter from the file header, and tempo is expressed in microseconds per MIDI quarter-note, or "24ths of a microsecond per MIDI clock". The division has two meanings, depending on whether bit 15 is set or not. If bit 15 of division is zero, bits 14 through 0 represent the number of delta-time "ticks" which make up a quarter note. If bit 15 of division is a one, delta-times in a file correspond to subdivisions of a second similar to SMPTE and MIDI time code. In this format bits 14 through 8 contain one of four values -24, -25, -29, or -30, corresponding to the four standard SMPTE and MIDI time code frame per second formats, where -29 represents 30 drop frame. The second byte consisting of bits 7 through 0 corresponds the the resolution within a frame. Refer the Standard MIDI Files 1.0 spec for more details.

WRITING EXAMPLE
The following is a simple program to demonstrate writing MIDI files. The track would consist of a series of quarter notes from lowest to highest in pitch at constant velocity, each separated by a quarter-note rest.

#include <stdio.h>
#include <ctype.h>
#include "midifile.h"

FILE *fp;
myputc(c) { return(putc(c,fp));}

int mywritetrack(track)
int track;
{
    int i;
    char data[2];

    /* 120 beats/per/second */
    mf_write_tempo((long)500000);

    for(i = 1 ; i < 128; i++){
       data[0] = i; /* note number */
       data[1] = 64; /* velocity */
       if(!mf_write_midi_event(480,note_on,1,data,2))
	   return(-1);
       if(!mf_write_midi_event(480,note_off,1,data,2))
           return(-1);
    }

    return(1);
} /* end of write_track() */

main(argc,argv)
char **argv;
{
    if((fp = fopen(argv[1],"w")) == 0L)
	exit(1);

    Mf_putc = myputc;
    Mf_writetrack = mywritetrack;

    /* write a single track */
    mfwrite(0,1,480,fp);
}

AUTHOR
Tim Thompson (att!twitch!glimmer!tjt)

CONTRIBUTORS
Michael Czeiszperger (mike@pan.com)