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 });

// All MIDI messages have been sent when the promise returned by play() resolves.
await midiPlayer.play();

By default only control change, note off, note on and program change 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.