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# aiSpeakStream

aiSpeakStream() streams synthesized speech to a callback as it is generated.

Stream text-to-speech audio from an AI provider as it is generated. See [Streaming Text-to-Speech](/main-components/audio/streaming-speech.md) for the full guide.

## Syntax

```javascript
summary = aiSpeakStream( text, callback, params={}, options={} )
```

## Parameters

| Parameter  | Type     | Required | Description                                                                                                                |
| ---------- | -------- | -------- | -------------------------------------------------------------------------------------------------------------------------- |
| `text`     | string   | ✅ Yes    | The text to synthesize. Must not be empty                                                                                  |
| `callback` | function | ✅ Yes    | Called with each event struct. Return `false` to stop early and close the provider connection                              |
| `params`   | struct   | No       | Provider parameters: `model`, `voice` (or `voice_id`), `sample_rate`, `language`, `add_timestamps`, `transport` (Cartesia) |
| `options`  | struct   | No       | `provider`, `apiKey`, `outputFormat`, `speed`, `timeout` (idle timeout in seconds, default 30), logging                    |

## Callback events

| `type`       | Fields                                              |
| ------------ | --------------------------------------------------- |
| `audio`      | `data` (binary), `format`, `sampleRate`, `sequence` |
| `timestamps` | `words`, `start`, `end`                             |
| `done`       | `chunks`, `bytes` (always last)                     |

## Returns

A struct: `{ provider, model, audioFormat, sampleRate, chunks, bytes, completed }`. `completed` is `false` when the callback stopped the stream.

## Throws

| Type                    | When                                                 |
| ----------------------- | ---------------------------------------------------- |
| `UnsupportedCapability` | The provider does not support streaming speech       |
| `InvalidArgument`       | Empty text, unsupported format, or invalid transport |
| `ProviderError`         | The provider returned an error                       |

## Examples

```javascript
// Restream pcm to a client
aiSpeakStream(
    "Hello!",
    ( event ) => { if ( event.type == "audio" ) socket.send( event.data ) },
    { voice: "female" },
    { provider: "cartesia", outputFormat: "pcm" }
)

// Fluent builder
summary = aiSpeak()
    .text( "Hello!" )
    .provider( "elevenlabs" )
    .asMP3()
    .stream( ( event ) => { /* ... */ } )
```

## Providers

Cartesia, ElevenLabs, OpenAI, Mistral and Gemini stream. Grok does not (WebSocket only). Check with `aiService( "cartesia" ).hasCapability( "speechStream" )`.

## See Also

* [aiSpeak](/advanced/reference/built-in-functions/aispeak.md)
* [Streaming Text-to-Speech](/main-components/audio/streaming-speech.md)


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