Add Dart API for Kokoro TTS models (#1723)

.github/scripts/test-dart.sh

@@ -7,6 +7,7 @@ cd dart-api-examples
 pushd tts
 
 echo '----------matcha tts----------'
+./run-kokoro-en.sh
 ./run-matcha-zh.sh
 ./run-matcha-en.sh
 ls -lh *.wav

dart-api-examples/tts/bin/kokoro-en.dart

@@ -0,0 +1,86 @@
+// Copyright (c)  2025  Xiaomi Corporation
+import 'dart:io';
+
+import 'package:args/args.dart';
+import 'package:sherpa_onnx/sherpa_onnx.dart' as sherpa_onnx;
+
+import './init.dart';
+
+void main(List<String> arguments) async {
+  await initSherpaOnnx();
+
+  final parser = ArgParser()
+    ..addOption('model', help: 'Path to the onnx model')
+    ..addOption('voices', help: 'Path to the voices.bin')
+    ..addOption('tokens', help: 'Path to tokens.txt')
+    ..addOption(
+      'data-dir',
+      help: 'Path to espeak-ng-data directory',
+      defaultsTo: '',
+    )
+    ..addOption('rule-fsts', help: 'Path to rule fsts', defaultsTo: '')
+    ..addOption('rule-fars', help: 'Path to rule fars', defaultsTo: '')
+    ..addOption('text', help: 'Text to generate TTS for')
+    ..addOption('output-wav', help: 'Filename to save the generated audio')
+    ..addOption('speed', help: 'Speech speed', defaultsTo: '1.0')
+    ..addOption(
+      'sid',
+      help: 'Speaker ID to select. Used only for multi-speaker TTS',
+      defaultsTo: '0',
+    );
+  final res = parser.parse(arguments);
+  if (res['model'] == null ||
+      res['voices'] == null ||
+      res['tokens'] == null ||
+      res['data-dir'] == null ||
+      res['output-wav'] == null ||
+      res['text'] == null) {
+    print(parser.usage);
+    exit(1);
+  }
+  final model = res['model'] as String;
+  final voices = res['voices'] as String;
+  final tokens = res['tokens'] as String;
+  final dataDir = res['data-dir'] as String;
+  final ruleFsts = res['rule-fsts'] as String;
+  final ruleFars = res['rule-fars'] as String;
+  final text = res['text'] as String;
+  final outputWav = res['output-wav'] as String;
+  var speed = double.tryParse(res['speed'] as String) ?? 1.0;
+  final sid = int.tryParse(res['sid'] as String) ?? 0;
+
+  if (speed == 0) {
+    speed = 1.0;
+  }
+
+  final kokoro = sherpa_onnx.OfflineTtsKokoroModelConfig(
+    model: model,
+    voices: voices,
+    tokens: tokens,
+    dataDir: dataDir,
+    lengthScale: 1 / speed,
+  );
+
+  final modelConfig = sherpa_onnx.OfflineTtsModelConfig(
+    kokoro: kokoro,
+    numThreads: 1,
+    debug: true,
+  );
+  final config = sherpa_onnx.OfflineTtsConfig(
+    model: modelConfig,
+    maxNumSenetences: 1,
+    ruleFsts: ruleFsts,
+    ruleFars: ruleFars,
+  );
+
+  final tts = sherpa_onnx.OfflineTts(config);
+  final audio = tts.generate(text: text, sid: sid, speed: speed);
+  tts.free();
+
+  sherpa_onnx.writeWave(
+    filename: outputWav,
+    samples: audio.samples,
+    sampleRate: audio.sampleRate,
+  );
+  print('Saved to $outputWav');
+}

dart-api-examples/tts/run-kokoro-en.sh

@@ -0,0 +1,27 @@
+#!/usr/bin/env bash
+
+set -ex
+
+dart pub get
+
+# please visit
+# https://k2-fsa.github.io/sherpa/onnx/tts/pretrained_models/kokoro.html
+# to download more models
+if [ ! -f ./kokoro-en-v0_19/model.onnx ]; then
+  curl -SL -O https://github.com/k2-fsa/sherpa-onnx/releases/download/tts-models/kokoro-en-v0_19.tar.bz2
+  tar xf kokoro-en-v0_19.tar.bz2
+  rm kokoro-en-v0_19.tar.bz2
+fi
+
+dart run \
+  ./bin/kokoro-en.dart \
+  --model ./kokoro-en-v0_19/model.onnx \
+  --voices ./kokoro-en-v0_19/voices.bin \
+  --tokens ./kokoro-en-v0_19/tokens.txt \
+  --data-dir ./kokoro-en-v0_19/espeak-ng-data \
+  --sid 9 \
+  --speed 1.0 \
+  --output-wav kokoro-en-9.wav \
+  --text "Friends fell out often because life was changing so fast. The easiest thing in the world was to lose touch with someone." \
+
+ls -lh *.wav

flutter/sherpa_onnx/lib/src/sherpa_onnx_bindings.dart

@@ -147,6 +147,16 @@ final class SherpaOnnxOfflineTtsMatchaModelConfig extends Struct {
   external Pointer<Utf8> dictDir;
 }
 
+final class SherpaOnnxOfflineTtsKokoroModelConfig extends Struct {
+  external Pointer<Utf8> model;
+  external Pointer<Utf8> voices;
+  external Pointer<Utf8> tokens;
+  external Pointer<Utf8> dataDir;
+
+  @Float()
+  external double lengthScale;
+}
+
 final class SherpaOnnxOfflineTtsModelConfig extends Struct {
   external SherpaOnnxOfflineTtsVitsModelConfig vits;
   @Int32()
@@ -157,6 +167,7 @@ final class SherpaOnnxOfflineTtsModelConfig extends Struct {
 
   external Pointer<Utf8> provider;
   external SherpaOnnxOfflineTtsMatchaModelConfig matcha;
+  external SherpaOnnxOfflineTtsKokoroModelConfig kokoro;
 }
 
 final class SherpaOnnxOfflineTtsConfig extends Struct {

flutter/sherpa_onnx/lib/src/tts.dart

@@ -60,10 +60,32 @@ class OfflineTtsMatchaModelConfig {
   final String dictDir;
 }
 
+class OfflineTtsKokoroModelConfig {
+  const OfflineTtsKokoroModelConfig({
+    this.model = '',
+    this.voices = '',
+    this.tokens = '',
+    this.dataDir = '',
+    this.lengthScale = 1.0,
+  });
+
+  @override
+  String toString() {
+    return 'OfflineTtsKokoroModelConfig(model: $model, voices: $voices, tokens: $tokens, dataDir: $dataDir, lengthScale: $lengthScale)';
+  }
+
+  final String model;
+  final String voices;
+  final String tokens;
+  final String dataDir;
+  final double lengthScale;
+}
+
 class OfflineTtsModelConfig {
   const OfflineTtsModelConfig({
     this.vits = const OfflineTtsVitsModelConfig(),
     this.matcha = const OfflineTtsMatchaModelConfig(),
+    this.kokoro = const OfflineTtsKokoroModelConfig(),
     this.numThreads = 1,
     this.debug = true,
     this.provider = 'cpu',
@@ -71,11 +93,12 @@ class OfflineTtsModelConfig {
 
   @override
   String toString() {
-    return 'OfflineTtsModelConfig(vits: $vits, matcha: $matcha, numThreads: $numThreads, debug: $debug, provider: $provider)';
+    return 'OfflineTtsModelConfig(vits: $vits, matcha: $matcha, kokoro: $kokoro, numThreads: $numThreads, debug: $debug, provider: $provider)';
   }
 
   final OfflineTtsVitsModelConfig vits;
   final OfflineTtsMatchaModelConfig matcha;
+  final OfflineTtsKokoroModelConfig kokoro;
   final int numThreads;
   final bool debug;
   final String provider;
@@ -138,6 +161,12 @@ class OfflineTts {
     c.ref.model.matcha.lengthScale = config.model.matcha.lengthScale;
     c.ref.model.matcha.dictDir = config.model.matcha.dictDir.toNativeUtf8();
 
+    c.ref.model.kokoro.model = config.model.kokoro.model.toNativeUtf8();
+    c.ref.model.kokoro.voices = config.model.kokoro.voices.toNativeUtf8();
+    c.ref.model.kokoro.tokens = config.model.kokoro.tokens.toNativeUtf8();
+    c.ref.model.kokoro.dataDir = config.model.kokoro.dataDir.toNativeUtf8();
+    c.ref.model.kokoro.lengthScale = config.model.kokoro.lengthScale;
+
     c.ref.model.numThreads = config.model.numThreads;
     c.ref.model.debug = config.model.debug ? 1 : 0;
     c.ref.model.provider = config.model.provider.toNativeUtf8();
@@ -151,12 +180,19 @@ class OfflineTts {
     calloc.free(c.ref.ruleFars);
     calloc.free(c.ref.ruleFsts);
     calloc.free(c.ref.model.provider);
+
+    calloc.free(c.ref.model.kokoro.dataDir);
+    calloc.free(c.ref.model.kokoro.tokens);
+    calloc.free(c.ref.model.kokoro.voices);
+    calloc.free(c.ref.model.kokoro.model);
+
     calloc.free(c.ref.model.matcha.dictDir);
     calloc.free(c.ref.model.matcha.dataDir);
     calloc.free(c.ref.model.matcha.tokens);
     calloc.free(c.ref.model.matcha.lexicon);
     calloc.free(c.ref.model.matcha.vocoder);
     calloc.free(c.ref.model.matcha.acousticModel);
+
     calloc.free(c.ref.model.vits.dictDir);
     calloc.free(c.ref.model.vits.dataDir);
     calloc.free(c.ref.model.vits.tokens);