Flutter音频处理插件dart_melty_soundfont的使用

简介

dart_melty_soundfont 是一个纯 Dart 编写的 SoundFont 合成器（即 ‘.sf2’ 播放器）。它是 Nobuaki Tanaka 使用 C# 编写的 MeltySynth 的 Dart 版本。更多关于MeltySynth

依赖项

此包没有外部依赖。

维护

该项目设计为无需维护，主要通过不引入任何依赖来实现这一点。除非 Dart 语言发生重大变更（这种情况很少见），否则代码应在未来数十年内保持稳定运行。它适用于任何版本大于等于2.12的Dart SDK。该包是在 Dart SDK 2.16.1 上编写的。

示例代码

示例1：合成简单和弦

// 必要的导入
import 'package:dart_melty_soundfont/dart_melty_soundfont.dart';
import 'package:flutter/services.dart' show rootBundle;

// 加载 sf2 文件
ByteData bytes = await rootBundle.load('assets/akai_steinway.sf2');

// 创建合成器
Synthesizer synth = Synthesizer.loadByteData(bytes, 
    SynthesizerSettings(
        sampleRate: 44100, 
        blockSize: 64, 
        maximumPolyphony: 64, 
        enableReverbAndChorus: true,
    ));

// 可选：打印可用乐器（即预设）
List<Preset> p = synth.soundFont.presets;
for (int i = 0; i < p.length; i++) {
  String instrumentName = p[i].regions.isNotEmpty ? p[i].regions[0].instrument.name : "N/A";
  print('[preset $i] name: ${p[i].name} instrument: $instrumentName');
}

// 可选：选择第一个乐器（即预设）
synth.selectPreset(channel: 0, preset: 0);

// 打开一些音符
synth.noteOn(channel: 0, key: 72, velocity: 120);
synth.noteOn(channel: 0, key: 76, velocity: 120);
synth.noteOn(channel: 0, key: 79, velocity: 120);
synth.noteOn(channel: 0, key: 82, velocity: 120);

// 创建 PCM 缓冲区
ArrayInt16 buf16 = ArrayInt16.zeros(numShorts: 44100 * 3);

// 渲染波形（1秒）
synth.renderMonoInt16(buf16);

// 关闭一个音符
synth.noteOff(channel: 0, key: 72, velocity: 120);

// 再渲染一秒
synth.renderMonoInt16(buf16);

示例2：从 MIDI 文件回放合成音符

// 必要的导入
import 'package:dart_melty_soundfont/dart_melty_soundfont.dart';
import 'package:flutter/services.dart' show rootBundle;

// 加载 soundfont 文件
ByteData bytes = await rootBundle.load('assets/akai_steinway.sf2');

// 创建合成器
Synthesizer synth = Synthesizer.loadByteData(bytes);

// 从资产加载 MIDI 文件
ByteData midiBytes = await rootBundle.load('assets/arabesque.mid');
MidiFile midiFile = MidiFile.fromByteData(midiBytes);

// 开始 MIDI 回放
MidiFileSequencer sequencer = MidiFileSequencer(synth);
sequencer.play(midiFile, loop: false);

// 更改回放速度。
sequencer.speed = 1.5;

// 将 10 秒的回放渲染到 PCM 缓冲区
ArrayInt16 buf16 = ArrayInt16.zeros(numShorts: 44100 * 10);
synth.renderMonoInt16(buf16);

示例应用：播放声音

这个库本身不会发出声音，它只生成 PCM 波形。要实际听到声音，你需要将生成的 PCM 波形传递给设备的扬声器。以下是一个完整的示例应用程序，结合了 flutter_pcm_sound 和 dart_melty_soundfont：

// ignore_for_file: avoid_print

import 'dart:typed_data'; // for Uint8List

import 'package:dart_melty_soundfont/preset.dart';
import 'package:flutter/services.dart' show rootBundle;

import 'package:flutter/material.dart';
import 'package:flutter_pcm_sound/flutter_pcm_sound.dart';

import 'package:dart_melty_soundfont/synthesizer.dart';
import 'package:dart_melty_soundfont/synthesizer_settings.dart';
import 'package:dart_melty_soundfont/audio_renderer_ex.dart';
import 'package:dart_melty_soundfont/array_int16.dart';

String asset = 'assets/TimGM6mbEdit.sf2';
int sampleRate = 44100;

void main() => runApp(const MeltyApp());

class MeltyApp extends StatefulWidget {
  const MeltyApp({Key? key}) : super(key: key);

  @override
  State<MeltyApp> createState() => _MyAppState();
}

class _MyAppState extends State<MeltyApp> {
  Synthesizer? _synth;

  bool _isPlaying = false;
  bool _pcmSoundLoaded = false;
  bool _soundFontLoaded = false;
  int _remainingFrames = 0;
  int _fedCount = 0;
  int _prevNote = 0;

  @override
  void initState() {
    super.initState();

    // DartMeltySoundfont
    _loadSoundfont().then((_) {
      _soundFontLoaded = true;
      setState(() {});
    });

    // FlutterPcmSound
    _loadPcmSound().then((_) {
      _pcmSoundLoaded = true;
      setState(() {});
    });
  }

  Future<void> _loadPcmSound() async {
    FlutterPcmSound.setFeedCallback(onFeed);
    await FlutterPcmSound.setLogLevel(LogLevel.standard);
    await FlutterPcmSound.setFeedThreshold(8000);
    await FlutterPcmSound.setup(sampleRate: sampleRate, channelCount: 1);
  }

  Future<void> _loadSoundfont() async {
    ByteData bytes = await rootBundle.load(asset);
    _synth = Synthesizer.loadByteData(bytes, SynthesizerSettings());

    // 打印可用乐器
    List<Preset> p = _synth!.soundFont.presets;
    for (int i = 0; i < p.length; i++) {
      String instrumentName = p[i].regions.isNotEmpty ? p[i].regions[0].instrument.name : "N/A";
      print('[preset $i] name: ${p[i].name} instrument: $instrumentName');
    }

    return Future<void>.value(null);
  }

  @override
  void dispose() {
    FlutterPcmSound.release();
    super.dispose();
  }

  void onFeed(int remainingFrames) async {
    setState(() {
      _remainingFrames = remainingFrames;
    });
    // C 大调音阶
    List<int> notes = [60, 62, 64, 65, 67, 69, 71, 72];
    int step = (_fedCount ~/ 16) % notes.length;
    int curNote = notes[step];
    if (curNote != _prevNote) {
      _synth!.noteOff(channel: 0, key: _prevNote);
      _synth!.noteOn(channel: 0, key: curNote, velocity: 120);
    }
    ArrayInt16 buf16 = ArrayInt16.zeros(numShorts: 1000);
    _synth!.renderMonoInt16(buf16);
    await FlutterPcmSound.feed(PcmArrayInt16(bytes: buf16.bytes));
    _fedCount++;
    _prevNote = curNote;
  }

  Future<void> _play() async {
    // 开始播放音频
    await FlutterPcmSound.play();

    setState(() {
      _isPlaying = true;
    });

    // 关闭所有音符
    _synth!.noteOffAll();

    // 选择预设（即乐器）
    _synth!.selectPreset(channel: 0, preset: 0);
  }

  Future<void> _pause() async {
    await FlutterPcmSound.pause();
    setState(() {
      _isPlaying = false;
    });
  }

  @override
  Widget build(BuildContext context) {
    Widget child;
    if (!_pcmSoundLoaded || !_soundFontLoaded) {
      child = const Text("initializing...");
    } else {
      child = Center(
        child: Column(
          children: [
            Padding(
              padding: const EdgeInsets.all(20.0),
              child: ElevatedButton(
                child: Text(_isPlaying ? "Pause" : "Play"),
                onPressed: () => _isPlaying ? _pause() : _play(),
              ),
            ),
            Padding(
              padding: const EdgeInsets.all(20.0),
              child: Text("Remaining Frames $_remainingFrames"),
            )
          ],
        ),
      );
    }
    return MaterialApp(
        home: Scaffold(
      appBar: AppBar(title: const Text('Soundfont')),
      body: child,
    ));
  }
}

注意事项

• 隔离：建议在隔离中或使用 compute 进行音频渲染，以保持 UI 响应迅速并防止音频抖动。
• 功能：此库支持多种音频合成和 MIDI 消息处理功能，如波形生成、包络生成、低通滤波、颤音 LFO、调制 LFO、混响、合唱等。

许可证

DartMeltySoundFont 在 MIT 许可下可用。

参考资料

• SoundFont® 技术规范
• Polyphone Soundfont Editor
• Freeverb by Jezar at Dreampoint

希望这些信息对你有所帮助！如果你有任何问题，请随时提问。