【Flutter】speech_to_textで音声入力し文字起こし

dependencies:
  speech_to_text: ^7.4.0

import 'package:speech_to_text/speech_to_text.dart' as stt;

class SpeechService {
  final stt.SpeechToText _speech = stt.SpeechToText();

  Future<bool> initialize({
    required void Function(bool isListening) onStatusChange,
    required void Function(String message) onError,
  }) {
    return _speech.initialize(
      onStatus: (status) => onStatusChange(status == 'listening'),
      onError: (error) => onError(error.errorMsg),
    );
  }

  /// 話した内容を、認識できた分だけ onResult に渡し続ける。
  /// 一区切り話し終えると isFinal が true になる。
  Future<void> listen({
    required void Function(String recognizedWords, bool isFinal) onResult,
    String? localeId,
  }) {
    return _speech.listen(
      onResult: (result) => onResult(result.recognizedWords, result.finalResult),
      listenOptions: stt.SpeechListenOptions(
        localeId: localeId,
        partialResults: true,
      ),
    );
  }

  Future<void> stop() => _speech.stop();
}

import 'dart:async';
import 'package:flutter/material.dart';
import '../services/speech_service.dart';

class VoiceInputPage extends StatefulWidget {
  const VoiceInputPage({super.key, required this.title});

  final String title;

  @override
  State<VoiceInputPage> createState() => _VoiceInputPageState();
}

class _VoiceInputPageState extends State<VoiceInputPage> {
  final SpeechService _speech = SpeechService();

  bool _speechEnabled = false;
  bool _isListening = false;
  Timer? _restartTimer;

  String _committedText = ''; // 話し終えて確定した分
  String _partialText = ''; // いま話している途中の分
  String _statusMessage = '';

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

  @override
  void dispose() {
    _restartTimer?.cancel();
    _speech.stop();
    super.dispose();
  }

  Future<void> _initSpeech() async {
    final available = await _speech.initialize(
      onStatusChange: _handleStatus,
      onError: _handleError,
    );
    if (!mounted) return;
    setState(() {
      _speechEnabled = available;
      if (!available) _statusMessage = 'この端末では音声認識を利用できません';
    });
    if (available) _listen();
  }

  Future<void> _listen() async {
    if (!mounted || !_speechEnabled || _isListening) return;
    await _speech.listen(onResult: _handleResult);
  }

  void _handleResult(String words, bool isFinal) {
    setState(() {
      if (isFinal) {
        _committedText = '$_committedText $words'.trim();
        _partialText = '';
      } else {
        _partialText = words;
      }
    });
  }

  // 認識が止まったら、少し待って聞き取り直す。
  void _handleStatus(bool listening) {
    if (!mounted) return;
    setState(() => _isListening = listening);
    if (!listening && _speechEnabled) {
      _restartTimer?.cancel();
      _restartTimer = Timer(const Duration(milliseconds: 300), _listen);
    }
  }

  void _handleError(String message) {
    if (!mounted) return;
    setState(() {
      _isListening = false;
      _statusMessage = '音声認識エラー: $message';
      // マイクの許可がないときは、やり直しても同じなので止める。
      if (message.contains('permission')) _speechEnabled = false;
    });
  }

  String get _displayText => '$_committedText $_partialText'.trim();

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: [
          Padding(
            padding: const EdgeInsets.only(right: 16),
            child: Icon(
              _isListening ? Icons.mic : Icons.mic_off,
              color: _isListening ? Colors.red : Colors.grey,
            ),
          ),
        ],
      ),
      body: Padding(
        padding: const EdgeInsets.all(16),
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: [
            Expanded(
              child: SingleChildScrollView(
                child: Text(
                  _displayText.isEmpty ? '話しかけてください' : _displayText,
                  style: Theme.of(context).textTheme.headlineSmall,
                ),
              ),
            ),
            Text(_statusMessage),
          ],
        ),
      ),
    );
  }
}

import 'package:flutter/material.dart';

import 'pages/voice_input_page.dart';

void main() {
  runApp(
    const MaterialApp(home: VoiceInputPage(title: '音声入力')),
  );
}