MidiFile.java

/*
  A simple Java class that writes a MIDI file

  (c)2011 Kevin Boone, all rights reserved
*/
package com.kevinboone.music;
import java.io.*;
import java.util.*;


public class MidiFile
{
  // Note lengths
  //  We are working with 32 ticks to the crotchet. So
  //  all the other note lengths can be derived from this
  //  basic figure. Note that the longest note we can
  //  represent with this code is one tick short of a 
  //  two semibreves (i.e., 8 crotchets)

  static final int SEMIQUAVER = 4;
  static final int QUAVER = 8;
  static final int CROTCHET = 16;
  static final int MINIM = 32;
  static final int SEMIBREVE = 64;

  // Standard MIDI file header, for one-track file
  // 4D, 54... are just magic numbers to identify the
  //  headers
  // Note that because we're only writing one track, we
  //  can for simplicity combine the file and track headers
  static final int header[] = new int[]
     {
     0x4d, 0x54, 0x68, 0x64, 0x00, 0x00, 0x00, 0x06,
     0x00, 0x00, // single-track format
     0x00, 0x01, // one track
     0x00, 0x10, // 16 ticks per quarter
     0x4d, 0x54, 0x72, 0x6B
     };

  // Standard footer
  static final int footer[] = new int[]
     {
     0x01, 0xFF, 0x2F, 0x00
     };

  // A MIDI event to set the tempo
  static final int tempoEvent[] = new int[]
     {
     0x00, 0xFF, 0x51, 0x03,
     0x0F, 0x42, 0x40 // Default 1 million usec per crotchet
     };

  // A MIDI event to set the key signature. This is irrelent to
  //  playback, but necessary for editing applications 
  static final int keySigEvent[] = new int[]
     {
     0x00, 0xFF, 0x59, 0x02,
     0x00, // C
     0x00  // major
     };


  // A MIDI event to set the time signature. This is irrelent to
  //  playback, but necessary for editing applications 
  static final int timeSigEvent[] = new int[]
     {
     0x00, 0xFF, 0x58, 0x04,
     0x04, // numerator
     0x02, // denominator (2==4, because it's a power of 2)
     0x30, // ticks per click (not used)
     0x08  // 32nd notes per crotchet 
     };

  // The collection of events to play, in time order
  protected Vector<int[]> playEvents;

  /** Construct a new MidiFile with an empty playback event list */
  public MidiFile()
  {
    playEvents = new Vector<int[]>();
  }


  /** Write the stored MIDI events to a file */
  public void writeToFile (String filename)
    throws IOException
  {
    FileOutputStream fos = new FileOutputStream (filename);


    fos.write (intArrayToByteArray (header));

    // Calculate the amount of track data
    // _Do_ include the footer but _do not_ include the 
    // track header

    int size = tempoEvent.length + keySigEvent.length + timeSigEvent.length
      + footer.length;

    for (int i = 0; i < playEvents.size(); i++)
      size += playEvents.elementAt(i).length;

    // Write out the track data size in big-endian format
    // Note that this math is only valid for up to 64k of data
    //  (but that's a lot of notes) 
    int high = size / 256;
    int low = size - (high * 256);
    fos.write ((byte) 0);
    fos.write ((byte) 0);
    fos.write ((byte) high);
    fos.write ((byte) low);


    // Write the standard metadata — tempo, etc
    // At present, tempo is stuck at crotchet=60 
    fos.write (intArrayToByteArray (tempoEvent));
    fos.write (intArrayToByteArray (keySigEvent));
    fos.write (intArrayToByteArray (timeSigEvent));

    // Write out the note, etc., events
    for (int i = 0; i < playEvents.size(); i++)
    {
      fos.write (intArrayToByteArray (playEvents.elementAt(i)));
    }

    // Write the footer and close
    fos.write (intArrayToByteArray (footer));
    fos.close();
  }


  /** Convert an array of integers which are assumed to contain
      unsigned bytes into an array of bytes */
  protected static byte[] intArrayToByteArray (int[] ints)
  {
    int l = ints.length;
    byte[] out = new byte[ints.length];
    for (int i = 0; i < l; i++)
    {
      out[i] = (byte) ints[i];
    }
    return out;
  }


  /** Store a note-on event */
  public void noteOn (int delta, int note, int velocity)
  {
  int[] data = new int[4];
  data[0] = delta;
  data[1] = 0x90;
  data[2] = note;
  data[3] = velocity;
  playEvents.add (data);
  }


  /** Store a note-off event */
  public void noteOff (int delta, int note)
  {
  int[] data = new int[4];
  data[0] = delta;
  data[1] = 0x80;
  data[2] = note;
  data[3] = 0;
  playEvents.add (data);
  }


  /** Store a program-change event at current position */
  public void progChange (int prog)
  {
  int[] data = new int[3];
  data[0] = 0;
  data[1] = 0xC0;
  data[2] = prog;
  playEvents.add (data);
  }


  /** Store a note-on event followed by a note-off event a note length
      later. There is no delta value — the note is assumed to
      follow the previous one with no gap. */
  public void noteOnOffNow (int duration, int note, int velocity)
  {
  noteOn (0, note, velocity);
  noteOff (duration, note);
  }


  public void noteSequenceFixedVelocity (int[] sequence, int velocity)
  {
    boolean lastWasRest = false;
    int restDelta = 0;
    for (int i = 0; i < sequence.length; i += 2)
    {
      int note = sequence[i];
      int duration = sequence[i + 1];
      if (note < 0)
      {
        // This is a rest
        restDelta += duration;
        lastWasRest = true;
      }
      else
      {
        // A note, not a rest
        if (lastWasRest)
        {
          noteOn (restDelta, note, velocity);
          noteOff (duration, note);
        }
        else
        {
          noteOn (0, note, velocity);
          noteOff (duration, note);
        }
        restDelta = 0;
        lastWasRest = false;
      }
    }
  }


  /** Test method — creates a file test1.mid when the class
      is executed */
  public static void main (String[] args)
    throws Exception
  {
    MidiFile mf = new MidiFile();

    // Test 1 — play a C major chord

    // Turn on all three notes at start-of-track (delta=0) 
    mf.noteOn (0, 60, 127);
    mf.noteOn (0, 64, 127);
    mf.noteOn (0, 67, 127);

    // Turn off all three notes after one minim. 
    // NOTE delta value is cumulative — only _one_ of
    //  these note-offs has a non-zero delta. The second and
    //  third events are relative to the first
    mf.noteOff (MINIM, 60);
    mf.noteOff (0, 64);
    mf.noteOff (0, 67);

    // Test 2 — play a scale using noteOnOffNow
    //  We don't need any delta values here, so long as one
    //  note comes straight after the previous one 

    mf.noteOnOffNow (QUAVER, 60, 127);
    mf.noteOnOffNow (QUAVER, 62, 127);
    mf.noteOnOffNow (QUAVER, 64, 127);
    mf.noteOnOffNow (QUAVER, 65, 127);
    mf.noteOnOffNow (QUAVER, 67, 127);
    mf.noteOnOffNow (QUAVER, 69, 127);
    mf.noteOnOffNow (QUAVER, 71, 127);
    mf.noteOnOffNow (QUAVER, 72, 127);

    // Test 3 — play a short tune using noteSequenceFixedVelocity
    //  Note the rest inserted with a note value of -1

    int[] sequence = new int[]
      {
      60, QUAVER + SEMIQUAVER,
      65, SEMIQUAVER,
      70, CROTCHET + QUAVER,
      69, QUAVER,
      65, QUAVER / 3,
      62, QUAVER / 3,
      67, QUAVER / 3,
      72, MINIM + QUAVER,
      -1, SEMIQUAVER,
      72, SEMIQUAVER,
      76, MINIM,
      };

    // What the heck — use a different instrument for a change
    mf.progChange (10);

    mf.noteSequenceFixedVelocity (sequence, 127);

    mf.writeToFile ("test1.mid");
  }
}