> ## Documentation Index
> Fetch the complete documentation index at: https://docs.runanywhere.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# Streaming TTS

> Stream audio for lower perceived latency

Stream TTS audio as it's generated for faster time-to-first-audio, especially with longer text.

## Overview

Streaming TTS starts playing audio before the entire synthesis is complete. This is particularly useful for:

* Long text passages
* Voice assistants responding in real-time
* Reducing perceived latency

## Basic Concept

```dart theme={null}
// The Voice Agent pipeline handles streaming TTS automatically
final session = await RunAnywhere.startVoiceSession(
  config: VoiceSessionConfig(
    autoPlayTTS: true,  // Automatically plays synthesized audio
  ),
);

session.events.listen((event) {
  if (event is VoiceSessionSpeaking) {
    print('Playing audio response...');
  }
});
```

## Chunked Synthesis

For manual control, synthesize text in chunks:

```dart theme={null}
Future<void> speakInChunks(String longText) async {
  // Split into sentences
  final sentences = longText.split(RegExp(r'(?<=[.!?])\s+'));

  for (final sentence in sentences) {
    final result = await RunAnywhere.synthesize(sentence);
    await playAudio(result);
  }
}
```

## With Voice Agent Pipeline

The Voice Agent provides the best streaming TTS experience:

```dart theme={null}
// Initialize all components
await RunAnywhere.loadSTTModel('sherpa-onnx-whisper-tiny.en');
await RunAnywhere.loadModel('smollm2-360m-q8_0');
await RunAnywhere.loadTTSVoice('vits-piper-en_US-lessac-medium');

// Start session with auto-play
final session = await RunAnywhere.startVoiceSession(
  config: VoiceSessionConfig(
    autoPlayTTS: true,
    continuousMode: true,
  ),
);

// The pipeline automatically:
// 1. Detects speech (VAD)
// 2. Transcribes audio (STT)
// 3. Generates response (LLM)
// 4. Synthesizes and plays audio (TTS)
session.events.listen((event) {
  switch (event) {
    case VoiceSessionTranscribed(:final text):
      print('User: $text');
    case VoiceSessionResponded(:final text):
      print('AI: $text');
    case VoiceSessionSpeaking():
      print('Playing response...');
    case VoiceSessionTurnCompleted():
      print('Ready for next turn');
    default:
      break;
  }
});
```

## Latency Optimization Tips

<AccordionGroup>
  <Accordion title="Preload Voice Model" icon="download">
    Load the TTS voice during app startup or idle time, not when the user first needs it.

    ```dart theme={null}
    // In app initialization
    await RunAnywhere.loadTTSVoice('vits-piper-en_US-lessac-medium');
    ```
  </Accordion>

  <Accordion title="Use Faster Voices" icon="bolt">
    Smaller voice models synthesize faster. Choose based on your quality/speed tradeoff.
  </Accordion>

  <Accordion title="Sentence-Level Streaming" icon="bars-staggered">
    For very long responses, synthesize and play sentence by sentence rather than waiting for the
    complete response.
  </Accordion>

  <Accordion title="Buffer Management" icon="database">
    Start playback as soon as you have enough audio buffered (typically 100-200ms).
  </Accordion>
</AccordionGroup>

## See Also

<CardGroup cols={2}>
  <Card title="synthesize()" icon="volume-high" href="/flutter/tts/synthesize">
    Basic synthesis
  </Card>

  <Card title="Voice Agent" icon="robot" href="/flutter/voice-agent">
    Complete voice pipeline
  </Card>
</CardGroup>