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midi-player

A MIDI player which sends MIDI messages to connected devices.

This module provides a player which sends MIDI messages to connected devices. It schedules the messages with a look ahead of about 500 milliseconds. It does not directly rely on the Web MIDI API but expects a MIDIOutput to be passed as constructor argument. But theoretically that could be anything which implements the same interface.

Usage

midi-player is published on npm and can be installed as usual.

npm install midi-player

The only exported function is a factory method to create new player instances.

import { create } from 'midi-player';

// This is a JSON object which represents a MIDI file.
const json = {
    division: 480,
    format: 1,
    tracks: [
        { channel: 0, delta: 0, noteOn: { noteNumber: 36, velocity: 100 } },
        { channel: 0, delta: 240, noteOff: { noteNumber: 36, velocity: 64 } },
        { delta: 0, endOfTrack: true }
    ]
};

// This is a quick & dirty approach to grab the first known MIDI output.
const midiAccess = await navigator.requestMIDIAccess();
const midiOutput = Array.from(midiAccess.outputs)[0];

const midiPlayer = create({ json, midiOutput });

By default all status events will be sent. But it's possible to provide a custom filter function. The following player will only send note off and note on events.

const midiPlayer = create({
    filterMidiMessage: (event) => 'noteOff' in event || 'noteOn' in event
    // ... other options as described above
});

If you want to play a binary MIDI file you can use the midi-json-parser package to transform it into a compatible JSON representation.

position

The position is set to the current position in milliseconds.

midiPlayer.position;

state

The state property will either be set to 'paused', 'playing', or 'stopped'.

midiPlayer.state;

play()

Calling play() will initiate the playback from the start.

midiPlayer.play().then(() => {
    // All MIDI messages have been sent when the promise returned by play() resolves.
});

It can only be called when the state of the player is 'stopped'.

pause()

Calling pause() will pause the playback at the current position.

midiPlayer.pause();

It can only be called when the state of the player is 'playing'.

resume()

Calling resume() will resume a previously paused playback at the current position.

midiPlayer.resume().then(() => {
    // All MIDI messages have been sent when the promise returned by resume() resolves.
});

It can only be called when the state of the player is 'paused'.

stop()

Calling stop() will stop the player.

midiPlayer.stop();

It can only be called when the state of the player is not 'stopped'.

Acknowledgement

Most of the features of this package have been originally developed by @infojunkie who maintains a midi-player fork (infojunkie/midi-player) with even more functionality.