flutter_tts

When using flutter_tts on iOS, you can manage the audio session to control how your app's speech interacts with other audio (like background music).

Use setIosAudioCategory to set the category, options, and mode. For example, to allow background music and in-app audio to play simultaneously, use IosTextToSpeechAudioCategory.ambient with IosTextToSpeechAudioCategoryOptions.mixWithOthers.

await flutterTts.setIosAudioCategory(
  IosTextToSpeechAudioCategory.ambient,
  [
    IosTextToSpeechAudioCategoryOptions.allowBluetooth,
    IosTextToSpeechAudioCategoryOptions.allowBluetoothA2DP,
    IosTextToSpeechAudioCategoryOptions.mixWithOthers
  ],
  IosTextToSpeechAudioMode.voicePrompt
);

Add flutter_tts to your pubspec.yaml dependencies file to use the plugin in your Flutter project.

dependencies:
  flutter:
    sdk: flutter
  flutter_tts:

To change the image displayed during the app's launch on iOS, you can either replace the image files directly in the example/ios/Runner/Assets.xcassets/LaunchImage.imageset/ directory or use Xcode for a more visual approach.

Using Xcode:

1. Open the iOS workspace in Xcode by running open ios/Runner.xcworkspace from your terminal.
2. In the Xcode Project Navigator, navigate to Runner/Assets.xcassets.
3. Drag and drop your desired images into the asset catalog.

On the Web, the plugin listens to the onBoundary event of the SpeechSynthesisUtterance. It calculates word boundaries by looking for whitespace or punctuation in the text following the charIndex provided by the browser.

When a word boundary is detected, it invokes the speak.onProgress method via the platform channel with the following payload:

The flutter_tts plugin on the Web uses the browser's SpeechSynthesis API via SpeechSynthesisUtterance.

Key Behaviors:

• Initialization: The plugin attempts to initialize SpeechSynthesisUtterance. If it fails, the supported flag is set to false, and subsequent method calls will not execute.
• State Management: The plugin tracks the speech state using TtsState (playing, stopped, paused, continued).
• Non-Local Service Workaround: For voices that are not local services (often remote cloud voices in browsers), the plugin implements a periodic timer that calls synth.pause() and synth.resume() every 14 seconds to prevent the browser from idling or timing out the speech session.

On iOS (13+) and Android, you can save the spoken text to a file. Note that file extensions may vary by platform (e.g., .wav for Android, .caf for iOS).

// iOS, macOS, and Android only
await flutterTts.synthesizeToFile(
  "Hello World", 
  Platform.isAndroid ? "tts.wav" : "tts.caf", 
  false
);

You can register handlers to respond to different stages of the text-to-speech lifecycle, such as when speech starts, completes, pauses, or encounters an error.

flutterTts.setStartHandler(() {
  // Triggered when speech starts
});

flutterTts.setCompletionHandler(() {
  // Triggered when speech finishes
});

flutterTts.setProgressHandler((String text, int startOffset, int endOffset, String word) {
  // Triggered during speech to provide progress and current word
});

flutterTts.setErrorHandler((msg) {
  // Triggered on error
});

flutterTts.setPauseHandler((msg) {
  // Triggered when speech is paused (Android, iOS, Web)
});

flutterTts.setContinueHandler((msg) {
  // Triggered when speech resumes (Android, iOS, Web)
});