I want to build an app that uses DartMeltySoundFont as a synthesizer and raw_sounds to play the sounds.

DartMeltySoundFont gives me a byte buffer in the type ArrayInt16 and raw_sounds expects Uint8List to play the audio.

I already asked the developer of DartMeltySoundFont but he does not have to to look into it.

This is an example app taken from raw_sound examples and added DartMeltySoundFont to it. Look at the line with the comment "// How do I return a Uint8List from buf16 here? "

import 'dart:typed_data'; // for Uint8List
import 'package:flutter/material.dart';
import 'package:raw_sound/raw_sound_player.dart';
import 'package:dart_melty_soundfont/dart_melty_soundfont.dart';
import 'package:flutter/services.dart' show rootBundle;

void main() {
  runApp(MyApp());
}

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  // Player instance to play raw PCM (16-bit integer) audio data
  final _playerPCMI16 = RawSoundPlayer();

  @override
  void initState() {
    super.initState();
    //  release any initialized player instances
    _playerPCMI16
        .initialize(
      pcmType: RawSoundPCMType.PCMI16,
    )
        .then((value) {
      setState(() {
        // Trigger rebuild to update UI
      });
    });
  }

  @override
  void dispose() {
    // Finally release any initialized player instances
    _playerPCMI16.release();
    super.dispose();
  }

  Future<void> _playPCMI16() async {
    if (_playerPCMI16.isPlaying) {
      return;
    }
    await _playerPCMI16.play();
    setState(() {
      // Trigger rebuild to update UI
    });
    // Continuously feed the player until the playback is paused/stopped
    //final dataBlock = _genPCMI16DataBlock(nPeriods: 20);
    final dataBlock = await _getSound();
    while (_playerPCMI16.isPlaying) {
      await _playerPCMI16.feed(dataBlock);
    }
  }

  Future<void> _pausePCMI16() async {
    await _playerPCMI16.pause();
    setState(() {
      // Trigger rebuild to update UI
    });
  }

  _getSound() async {
    // Create the synthesizer.
    ByteData bytes = await rootBundle.load('assets/akai_steinway.sf2');

    Synthesizer synth = Synthesizer.loadByteData(
        bytes,
        SynthesizerSettings(
          sampleRate: 44100,
          blockSize: 64,
          maximumPolyphony: 64,
          enableReverbAndChorus: true,
        ));

// Turn on some notes
    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);

// Render the waveform (3 seconds)
    ArrayInt16 buf16 = ArrayInt16.zeros(numShorts: 44100 * 3);

    synth.renderMonoInt16(buf16);

// How do I return a Uint8List from buf16 here?

  return null;
  }

  Widget build(BuildContext context) {
    debugPrint('PlayerPCMI16 is inited? ${_playerPCMI16.isInited}');

    if (!_playerPCMI16.isInited) {
      return Container();
    }

    return MaterialApp(
      theme: ThemeData(
        primarySwatch: Colors.grey,
      ),
      home: Scaffold(
        appBar: AppBar(
          centerTitle: true,
          title: Text('Raw Sound Plugin Example App'),
        ),
        body: Column(
          children: [
            Card(
              child: Row(
                children: [
                  IconButton(
                    icon: Icon(_playerPCMI16.isPlaying ? Icons.stop : Icons.play_arrow),
                    onPressed: () {
                      _playerPCMI16.isPlaying ? _pausePCMI16() : _playPCMI16();
                    },
                  ),
                  Text('Test PCMI16 (16-bit Integer)'),
                ],
              ),
            ),
          ],
        ),
      ),
    );
  }
}

CodePudding user response：

hey there just add below line in _getSound function.

var unit8list= buf16.bytes.buffer.asUint8List();

and return unit8list. it will work

Example:

    _getSound() async {
    // Create the synthesizer.
    ByteData bytes = await rootBundle.load('assets/akai_steinway.sf2');

    Synthesizer synth = Synthesizer.loadByteData(
        bytes,
        SynthesizerSettings(
          sampleRate: 44100,
          blockSize: 64,
          maximumPolyphony: 64,
          enableReverbAndChorus: true,
        ));

// Turn on some notes
    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);

// Render the waveform (3 seconds)
    ArrayInt16 buf16 = ArrayInt16.zeros(numShorts: 44100 * 3);

    synth.renderMonoInt16(buf16);
   var unit8list= buf16.bytes.buffer.asUint8List();
// How do I return a Uint8List from buf16 here?

    return unit8list;
  }