♬ MidiWriterJS

MidiWriterJS is a JavaScript library providing an API for generating expressive multi-track MIDI files.

Note that the master branch is in active development so if you're looking for a tried and true stable version please use the latest release.

Install

npm install midi-writer-js

Getting Started

var MidiWriter = require('midi-writer-js');

// Start with a new track
var track = new MidiWriter.Track();

// Define an instrument (optional):
track.addEvent(new MidiWriter.ProgramChangeEvent({instrument : 1}));

// Add some notes:
var note = new MidiWriter.NoteEvent({pitch:['C4', 'D4', 'E4'], duration: '4'});
track.addEvent(note);

// Generate a data URI
var write = new MidiWriter.Writer([track]);
console.log(write.dataUri());

Documentation

MidiWriter.Track()

• addEvent({event}, mapFunction)
• setTempo(tempo)
• addText(text)
• addCopyright(text)
• addInstrumentName(text)
• addMarker(text)
• addCuePoint(text)
• addLyric(text)
• setTimeSignature(numerator, denominator)

MidiWriter.NoteEvent({options})

The NoteEvent supports these options:

Name	Type	Description
pitch	array	An array of notes to be triggered. Can be a string or valid MIDI note code. Format for string is C#4. Pro tip: You can use the output from tonal functions to build scales, chords, intervals, etc. in this parameter.
duration	string	How long the note should sound. 1 : whole 2 : half d2 : dotted half 4 : quarter d4 : dotted quarter 8 : eighth 8t : eighth triplet d8 : dotted eighth 16 : sixteenth
wait	string	How long to wait before sounding note (rest). Takes same values as duration.
sequential	boolean	If true then array of notes will be played sequentially as opposed to simulatanously. Default: false
velocity	number	How loud the note should sound, values 1-100. Default: 50
repeat	number	How many times this event should be repeated. Default: 1
channel	number	MIDI channel to use. Default: 1

MidiWriter.Writer([tracks])

The Writer class provides a few ways to output the file:

• buildFile() Uint8Array
• base64() string
• dataUri() string
• stdout() file stream (cli)

Hot Cross Buns

Here's an example of how everyone's favorite song "Hot Cross Buns" could be written. Note use of the mapping function passed as the second argument of addEvent(). This can be used to apply specific properties to all events. With some street smarts you could also use it for programmatic crescendos and other property 'animation'.

var MidiWriter = require('midi-writer-js');

var track = new MidiWriter.Track();

track.addEvent([
			new MidiWriter.NoteEvent({pitch: ['E4','D4'], duration: '4'}),
			new MidiWriter.NoteEvent({pitch: ['C4'], duration: '2'}),
			new MidiWriter.NoteEvent({pitch: ['E4','D4'], duration: '4'}),
			new MidiWriter.NoteEvent({pitch: ['C4'], duration: '2'}),
			new MidiWriter.NoteEvent({pitch: ['C4', 'C4', 'C4', 'C4', 'D4', 'D4', 'D4', 'D4'], duration: '8'}),
			new MidiWriter.NoteEvent({pitch: ['E4','D4'], duration: '4'}),
			new MidiWriter.NoteEvent({pitch: ['C4'], duration: '2'})
	], function(event, index) {
    return {sequential:true};
  }
);

var write = new MidiWriter.Writer([track]);
console.log(write.dataUri());

VexFlow Integration

MidiWriterJS can export MIDI from VexFlow voices, though this feature is still experimental. Current usage is to use MidiWriter.VexFlow.trackFromVoice(voice) to create a MidiWriterJS Track object:

// ...VexFlow code defining notes
var voice = create_4_4_voice().addTickables(notes);

var track = MidiWriter.VexFlow.trackFromVoice(voice);
var writer = new MidiWriter.Writer([track]);
console.log(writer.dataUri());