Async

Text-to-speech services using Async’s WebSocket and HTTP APIs

Overview

Async provides high-quality text-to-speech synthesis with two service implementations: AsyncAITTSService (WebSocket-based) for real-time streaming with interruption support, and AsyncAIHttpTTSService (HTTP-based) for simpler synthesis. AsyncAITTSService is recommended for interactive applications requiring low latency.

AsyncAI TTS API Reference

Pipecat’s API methods for AsyncAI TTS integration

Example Implementation

Complete example with WebSocket streaming

Async Documentation

Official Async API documentation

Voice Models

Explore available voice models and features

Installation

To use Async services, install the required dependencies:

pip install "pipecat-ai[asyncai]"

Prerequisites

Async Account Setup

Before using Async TTS services, you need:

1. Async Account: Sign up at Async
2. API Key: Generate an API key from your account dashboard
3. Voice Selection: Choose from available voice models

Required Environment Variables

• ASYNCAI_API_KEY: Your Async API key for authentication

Configuration

AsyncAITTSService

api_key · str · required

Async API key.

voice_id · str · required · deprecated

UUID of the voice to use for synthesis. Deprecated in v0.0.105. Use settings=AsyncAITTSService.Settings(voice=...) instead.

model · str · default: "async_flash_v1.0" · deprecated

TTS model to use. Deprecated in v0.0.105. Use settings=AsyncAITTSService.Settings(model=...) instead.

version · str · default: "v1"

Async API version.

url · str · default: "wss://api.async.com/text_to_speech/websocket/ws"

WebSocket endpoint URL.

sample_rate · int · default: "None"

Output audio sample rate in Hz. When None, uses the pipeline’s configured sample rate.

encoding · str · default: "pcm_s16le"

Audio encoding format.

container · str · default: "raw"

Audio container format.

text_aggregation_mode · TextAggregationMode · default: "TextAggregationMode.SENTENCE"

Controls how incoming text is aggregated before synthesis. SENTENCE (default) buffers text until sentence boundaries, producing more natural speech. TOKEN streams tokens directly for lower latency. Import from pipecat.services.tts_service.

aggregate_sentences · bool · default: "None" · deprecated

Deprecated in v0.0.104. Use text_aggregation_mode instead.

params · InputParams · default: "None" · deprecated

Deprecated in v0.0.105. Use settings=AsyncAITTSService.Settings(...) instead.

settings · AsyncAITTSService.Settings · default: "None"

Runtime-configurable settings. See Settings below.

AsyncAIHttpTTSService

The HTTP service accepts similar parameters to the WebSocket service, with these differences:

aiohttp_session · aiohttp.ClientSession · required

An aiohttp session for HTTP requests. You must create and manage this yourself.

url · str · default: "https://api.async.com"

HTTP API base URL (instead of WebSocket URL).

Settings

Runtime-configurable settings passed via the settings constructor argument using AsyncAITTSService.Settings(...). These can be updated mid-conversation with TTSUpdateSettingsFrame. See Service Settings for details.

Parameter	Type	Default	Description
model	str	None	Model identifier. (Inherited.)
voice	str	None	Voice identifier. (Inherited.)
language	Language | str	None	Language for synthesis. (Inherited.)

Usage

Basic Setup

from pipecat.services.asyncai import AsyncAITTSService

tts = AsyncAITTSService(
    api_key=os.getenv("ASYNCAI_API_KEY"),
    settings=AsyncAITTSService.Settings(
        voice="your-voice-uuid",
    ),
)

With Language Customization

from pipecat.transcriptions.language import Language

tts = AsyncAITTSService(
    api_key=os.getenv("ASYNCAI_API_KEY"),
    settings=AsyncAITTSService.Settings(
        voice="your-voice-uuid",
        model="async_flash_v1.0",
        language=Language.ES,
    ),
)

HTTP Service

import aiohttp
from pipecat.services.asyncai import AsyncAIHttpTTSService

async with aiohttp.ClientSession() as session:
    tts = AsyncAIHttpTTSService(
        api_key=os.getenv("ASYNCAI_API_KEY"),
        settings=AsyncAIHttpTTSService.Settings(
            voice="your-voice-uuid",
        ),
        aiohttp_session=session,
    )

The InputParams / params= pattern is deprecated as of v0.0.105. Use Settings / settings= instead. See the Service Settings guide for migration details.

Event Handlers

Async TTS supports the standard service connection events:

Event	Description
on_connected	Connected to Async WebSocket
on_disconnected	Disconnected from Async WebSocket
on_connection_error	WebSocket connection error occurred

@tts.event_handler("on_connected")
async def on_connected(service):
    print("Connected to Async")