Flutter MIDI Engine

An advanced MIDI synthesizer plugin for Flutter with comprehensive support for SF2 and SF3 soundfont formats.

Features

  • Multi-Format Support: Load and play SF2 and SF3 soundfont files
  • Multi-Channel MIDI: Full 16-channel MIDI support for complex arrangements
  • Program Changes: Switch between 128 different instruments per soundfont
  • Audio Effects: Built-in reverb and chorus effects
  • Complete MIDI Control:
    • Note on/off with velocity
    • Volume and pan control per channel
    • Pitch bend messages
    • Control change messages
    • All notes off / reset controllers
  • Cross-Platform: Works on Android, iOS, and Web (Web support is experimental)

Platform Support

Platform Status Technology
Android ✅ Fully Supported MidiDriver (FluidSynth-based)
iOS ✅ Fully Supported AVFoundation AudioUnit Sampler
Web ⚠️ Experimental Stub implementation (requires JS library)
macOS 🚧 Planned Similar to iOS
Windows 🚧 Planned -
Linux 🚧 Planned -

Installation

Add this to your package's pubspec.yaml file:

dependencies:
  flutter_midi_engine: ^0.1.0

Getting Started

1. Add a Soundfont to Your Project

Place your SF2 or SF3 soundfont file in your assets folder:

flutter:
  assets:
    - assets/soundfonts/piano.sf2

2. Basic Usage

import 'package:flutter_midi_engine/flutter_midi_engine.dart';

final midiEngine = FlutterMidiEngine();

// Load a soundfont from assets
await midiEngine.loadSoundfontFromAsset('assets/soundfonts/piano.sf2');

// Play middle C
await midiEngine.playNote(note: 60, velocity: 100);

// Wait a bit
await Future.delayed(Duration(seconds: 1));

// Stop the note
await midiEngine.stopNote(note: 60);

3. Advanced Features

Change Instruments

// Change to Church Organ (program 19)
await midiEngine.changeProgram(program: 19);

// Play on different channels with different instruments
await midiEngine.changeProgram(program: 0, channel: 0);  // Piano on channel 0
await midiEngine.changeProgram(program: 40, channel: 1); // Violin on channel 1

await midiEngine.playNote(note: 60, channel: 0);
await midiEngine.playNote(note: 67, channel: 1);

Add Audio Effects

// Set reverb (hall effect)
await midiEngine.setReverb(
  roomSize: 0.8,
  damping: 0.3,
  width: 1.0,
  level: 0.5,
);

// Set chorus
await midiEngine.setChorus(
  voices: 5,
  level: 0.7,
  speed: 0.5,
  depth: 1.0,
);

Volume and Pan Control

// Set volume for channel 0
await midiEngine.setVolume(volume: 100, channel: 0);

// Pan channel 1 to the right
await midiEngine.setPan(pan: 127, channel: 1);

Pitch Bend

// Bend pitch up
await midiEngine.sendPitchBend(value: 4096, channel: 0);

// Reset to center
await midiEngine.sendPitchBend(value: 0, channel: 0);

Control Changes

// Enable sustain pedal
await midiEngine.sendControlChange(controller: 64, value: 127);

// Disable sustain pedal
await midiEngine.sendControlChange(controller: 64, value: 0);

iOS Setup

For iOS, you need to ensure the app can play audio even when the device is muted:

// Call this before loading the soundfont
await midiEngine.unmute();
await midiEngine.loadSoundfontFromAsset('assets/soundfonts/piano.sf2');

Example App

Check out the example directory for a complete piano app demonstrating all features.

MIDI Note Reference

MIDI notes range from 0 to 127, where:

  • Middle C (C4) = 60
  • A4 (440 Hz) = 69

Formula: MIDI Note = 12 * octave + semitone + 12

General MIDI Program Numbers

Some common instrument program numbers:

Program Instrument
0 Acoustic Grand Piano
4 Electric Piano 1
19 Church Organ
24 Acoustic Guitar (nylon)
40 Violin
56 Trumpet
73 Flute

See the full General MIDI specification for all 128 instruments.

Soundfont Resources

Free soundfonts you can use:

API Reference

Core Methods

  • loadSoundfont(String path) - Load soundfont from file path
  • loadSoundfontFromAsset(String assetPath) - Load soundfont from assets
  • unloadSoundfont() - Unload current soundfont
  • playNote({required int note, int velocity, int channel}) - Play MIDI note
  • stopNote({required int note, int velocity, int channel}) - Stop MIDI note

Instrument Control

  • changeProgram({required int program, int channel}) - Change instrument

Effects & Mix

  • setVolume({required int volume, int channel}) - Set channel volume (0-127)
  • setPan({required int pan, int channel}) - Set stereo pan (0=left, 64=center, 127=right)
  • setReverb({double roomSize, double damping, double width, double level}) - Configure reverb
  • setChorus({int voices, double level, double speed, double depth}) - Configure chorus

MIDI Control

  • sendControlChange({required int controller, required int value, int channel}) - Send CC message
  • sendPitchBend({required int value, int channel}) - Send pitch bend (-8192 to 8191)
  • stopAllNotes() - Stop all playing notes
  • resetAllControllers() - Reset all MIDI controllers

iOS-Specific

  • unmute() - Allow audio playback even when device is muted

Troubleshooting

Android

Issue: No sound on Android

  • Make sure you've called loadSoundfont() with a valid SF2/SF3 file
  • Check that the soundfont file exists in your assets
  • Verify device volume is turned up

iOS

Issue: No sound on iOS

  • Call unmute() before loading soundfont
  • Test on a real device (simulator has limited MIDI support)
  • Ensure SF2 file is properly formatted (SF3 support may vary)

Issue: Soundfont not found

  • Verify the file path is correct
  • When using assets, make sure the file is listed in pubspec.yaml

Contributing

Contributions are welcome! Please feel free to submit a Pull Request.

License

This project is licensed under the MIT License - see the LICENSE file for details.

Credits

Built with:

Libraries

flutter_midi_engine
flutter_midi_engine_web