TTS example using setProgressHandler

ttsSetProgressHandler.dart

import 'dart:async';
import 'dart:io' show Platform;
import 'package:flutter/foundation.dart' show kIsWeb;

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

void main() => runApp(MyApp());

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

enum TtsState { playing, stopped, paused, continued }

class _MyAppState extends State<MyApp> {
  late FlutterTts flutterTts;
  dynamic languages;
  String? language;
  double volume = 0.5;
  double pitch = 1.0;
  double rate = 0.5;
  bool isCurrentLanguageInstalled = false;
  int start = 0;
  int end = 0;

  String? _newVoiceText;

  TtsState ttsState = TtsState.stopped;

  get isPlaying => ttsState == TtsState.playing;
  get isStopped => ttsState == TtsState.stopped;
  get isPaused => ttsState == TtsState.paused;
  get isContinued => ttsState == TtsState.continued;

  bool get isIOS => !kIsWeb && Platform.isIOS;
  bool get isAndroid => !kIsWeb && Platform.isAndroid;
  bool get isWeb => kIsWeb;

  @override
  initState() {
    super.initState();
    initTts();
  }

  initTts() {
    flutterTts = FlutterTts();

    _getLanguages();

    if (isAndroid) {
      _getEngines();
    }

    flutterTts.setStartHandler(() {
      setState(() {
        print("Playing");
        ttsState = TtsState.playing;
      });
    });

    flutterTts.setCompletionHandler(() {
      setState(() {
        print("Complete");
        ttsState = TtsState.stopped;
      });
    });

    flutterTts.setCancelHandler(() {
      setState(() {
        print("Cancel");
        ttsState = TtsState.stopped;
      });
    });

    if (isWeb || isIOS) {
      flutterTts.setPauseHandler(() {
        setState(() {
          print("Paused");
          ttsState = TtsState.paused;
        });
      });

      flutterTts.setContinueHandler(() {
        setState(() {
          print("Continued");
          ttsState = TtsState.continued;
        });
      });
    }

    flutterTts.setErrorHandler((msg) {
      setState(() {
        print("error: $msg");
        ttsState = TtsState.stopped;
      });
    });

    flutterTts.setProgressHandler(
        (String text, int startOffset, int endOffset, String word) {
      setState(() {
        start = startOffset;
        end = endOffset;
      });
    });
  }

  Future _getLanguages() async {
    languages = await flutterTts.getLanguages;
    if (languages != null) setState(() => languages);
  }

  Future _getEngines() async {
    var engines = await flutterTts.getEngines;
    if (engines != null) {
      for (dynamic engine in engines) {
        print(engine);
      }
    }
  }

  Future _speak() async {
    await flutterTts.setVolume(volume);
    await flutterTts.setSpeechRate(rate);
    await flutterTts.setPitch(pitch);

    if (_newVoiceText != null) {
      await flutterTts.awaitSpeakCompletion(true);
      await flutterTts.speak(_newVoiceText!);
    }
  }

  Future _stop() async {
    var result = await flutterTts.stop();
    if (result == 1) setState(() => ttsState = TtsState.stopped);
  }

  Future _pause() async {
    var result = await flutterTts.pause();
    if (result == 1) setState(() => ttsState = TtsState.paused);
  }

  @override
  void dispose() {
    super.dispose();
    flutterTts.stop();
  }

  List<DropdownMenuItem<String>> getLanguageDropDownMenuItems() {
    var items = <DropdownMenuItem<String>>[];
    for (dynamic type in languages) {
      items.add(DropdownMenuItem(value: type as String, child: Text(type)));
    }
    return items;
  }

  void changedLanguageDropDownItem(String? selectedType) {
    setState(() {
      language = selectedType;
      flutterTts.setLanguage(language!);
      if (isAndroid) {
        flutterTts
            .isLanguageInstalled(language!)
            .then((value) => isCurrentLanguageInstalled = (value as bool));
      }
    });
  }

  void _onChange(String text) {
    setState(() {
      _newVoiceText = text;
    });
  }

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
        home: Scaffold(
            appBar: AppBar(
              title: Text('Flutter TTS'),
            ),
            body: SingleChildScrollView(
                scrollDirection: Axis.vertical,
                child: Column(children: [
                  _inputSection(),
                  ttsState == TtsState.playing
                      ? _textFromInput(start, end)
                      : Text(""),
                  _btnSection(),
                  languages != null ? _languageDropDownSection() : Text(""),
                  _buildSliders()
                ]))));
  }

  Widget _inputSection() => Container(
      alignment: Alignment.topCenter,
      padding: EdgeInsets.only(top: 25.0, left: 25.0, right: 25.0),
      child: TextField(
        onChanged: (String value) {
          _onChange(value);
          start = 0;
          end = value.length;
        },
      ));

  Widget _textFromInput(int start, int end) => Container(
      alignment: Alignment.topCenter,
      padding: EdgeInsets.only(top: 25.0, left: 25.0, right: 25.0),
      child: RichText(
        textAlign: TextAlign.center,
        text: TextSpan(children: <TextSpan>[
          TextSpan(
              text: _newVoiceText != null && start != 0
                  ? _newVoiceText!.substring(0, start)
                  : "",
              style: TextStyle(color: Colors.black)),
          TextSpan(
              text: _newVoiceText != null
                  ? _newVoiceText!.substring(start, end)
                  : "",
              style: TextStyle(color: Colors.red, fontWeight: FontWeight.bold)),
          TextSpan(
              text: _newVoiceText != null ? _newVoiceText!.substring(end) : "",
              style: TextStyle(color: Colors.black)),
        ]),
      ));

  Widget _btnSection() {
    if (isAndroid) {
      return Container(
          padding: EdgeInsets.only(top: 50.0),
          child:
              Row(mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [
            _buildButtonColumn(Colors.green, Colors.greenAccent,
                Icons.play_arrow, 'PLAY', _speak),
            _buildButtonColumn(
                Colors.red, Colors.redAccent, Icons.stop, 'STOP', _stop),
          ]));
    } else {
      return Container(
          padding: EdgeInsets.only(top: 50.0),
          child:
              Row(mainAxisAlignment: MainAxisAlignment.spaceEvenly, children: [
            _buildButtonColumn(Colors.green, Colors.greenAccent,
                Icons.play_arrow, 'PLAY', _speak),
            _buildButtonColumn(
                Colors.red, Colors.redAccent, Icons.stop, 'STOP', _stop),
            _buildButtonColumn(
                Colors.blue, Colors.blueAccent, Icons.pause, 'PAUSE', _pause),
          ]));
    }
  }

  Widget _languageDropDownSection() => Container(
      padding: EdgeInsets.only(top: 50.0),
      child: Row(mainAxisAlignment: MainAxisAlignment.center, children: [
        DropdownButton(
          value: language,
          items: getLanguageDropDownMenuItems(),
          onChanged: changedLanguageDropDownItem,
        ),
        Visibility(
          visible: isAndroid,
          child: Text("Is installed: $isCurrentLanguageInstalled"),
        ),
      ]));

  Column _buildButtonColumn(Color color, Color splashColor, IconData icon,
      String label, Function func) {
    return Column(
        mainAxisSize: MainAxisSize.min,
        mainAxisAlignment: MainAxisAlignment.center,
        children: [
          IconButton(
              icon: Icon(icon),
              color: color,
              splashColor: splashColor,
              onPressed: () => func()),
          Container(
              margin: const EdgeInsets.only(top: 8.0),
              child: Text(label,
                  style: TextStyle(
                      fontSize: 12.0,
                      fontWeight: FontWeight.w400,
                      color: color)))
        ]);
  }

  Widget _buildSliders() {
    return Column(
      children: [_volume(), _pitch(), _rate()],
    );
  }

  Widget _volume() {
    return Slider(
        value: volume,
        onChanged: (newVolume) {
          setState(() => volume = newVolume);
        },
        min: 0.0,
        max: 1.0,
        divisions: 10,
        label: "Volume: $volume");
  }

  Widget _pitch() {
    return Slider(
      value: pitch,
      onChanged: (newPitch) {
        setState(() => pitch = newPitch);
      },
      min: 0.5,
      max: 2.0,
      divisions: 15,
      label: "Pitch: $pitch",
      activeColor: Colors.red,
    );
  }

  Widget _rate() {
    return Slider(
      value: rate,
      onChanged: (newRate) {
        setState(() => rate = newRate);
      },
      min: 0.0,
      max: 1.0,
      divisions: 10,
      label: "Rate: $rate",
      activeColor: Colors.green,
    );
  }
}

Hi , This code is working for English Language, speech and word highlight are in sync.
My language is Tamil, when I use this code speech and word highlight are not in sync for Tamil language. How to sync?

@ThirstyNeuronsTeam which device are you using?

One Plus Android v12