# Resemble AI

> Text-to-speech with Resemble AI: ResembleAITTSService streams audio and word timestamps over WebSocket.

Source: https://polvallverdu.github.io/pipedog/docs/services/tts/resembleai/



## Overview [#overview]

`ResembleAITTSService` keeps one WebSocket open to Resemble AI's streaming endpoint and sends each sentence as a JSON request. Audio comes back as base64 JSON frames, which the service buffers (a one-second jitter buffer first, then 2208-byte frames) so playback survives Resemble's bursty delivery.

<Cards>
  <Card title="Upstream page" href="https://docs.pipecat.ai/api-reference/server/services/tts/resembleai">
    Pipecat's documentation for the same service.
  </Card>

  <Card title="Source" href="https://github.com/polvallverdu/pipedog/tree/main/packages/resembleai/src">
    `packages/resembleai/src/tts.ts`.
  </Card>

  <Card title="Resemble AI docs" href="https://docs.resemble.ai/voice-generation/text-to-speech/streaming-websocket">
    The streaming WebSocket reference.
  </Card>
</Cards>

## Installation [#installation]

```bash
bun add @pipedog/resembleai
```

```ts
import { ResembleAITTSService } from "@pipedog/resembleai/tts";
```

## Prerequisites [#prerequisites]

* A Resemble AI account on a plan that includes the WebSocket API, an API key, and the UUID of a voice.
* Pass the key as `apiKey`. The examples read it from `RESEMBLE_API_KEY`.

## Configuration [#configuration]

| Option | Type | Required | Description |
|---|---|---|---|
| `apiKey` | `string` | yes | Resemble AI API key for authentication. |
| `url` | `string \| undefined` | no | WebSocket URL for Resemble AI TTS API. |
| `precision` | `string \| null \| undefined` | no | PCM bit depth (PCM_32, PCM_24, PCM_16, or MULAW). |
| `outputFormat` | `string \| null \| undefined` | no | Audio format (wav or mp3). |
| `projectUuid` | `string \| null \| undefined` | no | Project to attach the clips to. DIVERGENCE: not an upstream option. Resemble's WebSocket reference lists `project_uuid` as required, but upstream never sends it. It is sent only when this is set. |
| `settings` | `ResembleAITTSSettings \| null \| undefined` | no | Runtime-updatable settings. |
| `name` | `string \| null \| undefined` | no | Custom name; defaults to `ClassName#count`. |
| `taskManager` | `BaseTaskManager \| null \| undefined` | no | Task manager for handling tasks. |
| `enableDirectMode` | `boolean \| undefined` | no | Process frames immediately instead of using internal queues. |
| `metrics` | `FrameProcessorMetrics \| null \| undefined` | no | Optional metrics collector for this processor. |
| `reconnectBackoffMinWait` | `number \| undefined` | no | Minimum time, in seconds, to wait between reconnection attempts. |
| `reconnectBackoffMaxWait` | `number \| undefined` | no | Maximum time, in seconds, to wait between reconnection attempts. |
| `reconnectOnError` | `boolean \| undefined` | no | Whether to automatically reconnect on connection errors. |
| `wsCloseTimeout` | `number \| undefined` | no | Maximum time, in seconds, to wait for the peer to acknowledge the websocket closing handshake before dropping the connection. Applied to connections opened through `_websocketConnect()`. Increase it for peers that need longer to complete a graceful close. |
| `wsSendTimeout` | `number \| null \| undefined` | no | Maximum time, in seconds, a single send may wait on a peer that has stopped reading before the connection is dropped and the send throws `ConnectionClosedError`. Applied to connections opened through `_websocketConnect()`. Pass `null` to wait indefinitely. Defaults to `WS_SEND_TIMEOUT`. |
| `textAggregationMode` | `TextAggregationMode \| null \| undefined` | no | How to aggregate incoming text before synthesis. `TextAggregationMode.SENTENCE` (default) buffers until sentence boundaries, `TextAggregationMode.TOKEN` streams tokens directly for lower latency. |
| `pushTextFrames` | `boolean \| undefined` | no | Whether to push TextFrames and LLMFullResponseEndFrames. |
| `pushStopFrames` | `boolean \| undefined` | no | Whether to automatically push TTSStoppedFrames. |
| `pushStartFrame` | `boolean \| undefined` | no | Whether to automatically create audio contexts and push TTSStartedFrames. When true, the base class handles `createAudioContext` and yields `TTSStartedFrame` before each synthesis call, so `runTts` implementations do not need to. |
| `stopFrameTimeoutS` | `number \| undefined` | no | Idle time before pushing TTSStoppedFrame when pushStopFrames is true. |
| `pushSilenceAfterStop` | `boolean \| undefined` | no | Whether to push silence audio after TTSStoppedFrame. |
| `silenceTimeS` | `number \| undefined` | no | Duration of silence to push when pushSilenceAfterStop is true. |
| `pauseFrameProcessing` | `boolean \| undefined` | no | Whether to hold incoming frames after a turn until its audio contexts end. Needed by services whose audio doesn't carry its request's context ID. |
| `maxConsecutiveZeroAudioContexts` | `number \| undefined` | no | How many consecutive TTS contexts may complete without producing any audio before the service is reported unable to do its job. Catches a provider that accepts requests and stays silent — an unknown voice ID, say — which no error ever surfaces. Every silent context reports an error the service can carry on from, whatever the limit is; on reaching the limit the service reports a permanent error instead, stops being given work, and the pipeline worker applies its `ProcessorUnusablePolicy`. Set to 0 to report silent contexts without ever writing the service off. |
| `appendTrailingSpace` | `boolean \| undefined` | no | Whether to append a trailing space to text before sending to TTS. This helps prevent some TTS services from vocalizing trailing punctuation (e.g., "dot"). Only applied in sentence aggregation mode; when streaming tokens, the incoming text's own whitespace is preserved. |
| `sampleRate` | `number \| null \| undefined` | no | Output sample rate for generated audio. |
| `skipTextTypes` | `string[] \| null \| undefined` | no | List of text types that should not be spoken. |
| `textTransforms` | `[string, TextTransform][] \| null \| undefined` | no | A list of TextTransforms to transform text just before sending it to TTS. Each TextTransform takes the aggregated text and its type, and returns the transformed text. To register, provide a list of tuples of `[textType \| "*", transformFunction]`. |
| `transportDestination` | `string \| null \| undefined` | no | Destination for generated audio frames. |
| `reuseContextIdWithinTurn` | `boolean \| undefined` | no | Whether the service should reuse context IDs within the same turn. |
| `audioCache` | `TTSAudioCacheStore \| null \| undefined` | no | Where to keep synthesized audio for reuse (e.g. a shared `TTSAudioCache`). Text whose audio is in the cache is served from it, with no request to the provider. Lines get there through `warmAudioCache()`, and also from live synthesis when `cacheSynthesizedAudio` allows it. Only services that yield their audio from `runTts` (HTTP and streaming-RPC services, see `supportsAudioCache`) use it, and only in sentence aggregation mode. Defaults to null (no cache). pipedog only. |
| `cacheSynthesizedAudio` | `boolean \| ((text: string) => boolean) \| undefined` | no | Whether audio synthesized live is stored in `audioCache`, or a function that decides per text. Defaults to false: only warmed lines are stored, since a generated reply can repeat what the user said. pipedog only. |
| `audioCacheNamespace` | `string \| undefined` | no | Extra part of the cache key, for constructor options that change the audio but are not in `settings`. pipedog only. |

### Settings [#settings]

Runtime-updatable settings, passed as `settings: new ResembleAITTSService.Settings({...})`
(`ResembleAITTSSettings`). Any setting you leave out keeps the default below.

| Setting    | Type               | Default | Description                       |
| ---------- | ------------------ | ------- | --------------------------------- |
| `voice`    | `string \| null`   | `null`  | UUID of the voice (`voice_uuid`). |
| `model`    | `string \| null`   | `null`  | Not used.                         |
| `language` | `Language \| null` | `null`  | Not used.                         |

## Usage [#usage]

```ts title="tts.ts"
import { ResembleAITTSService } from "@pipedog/resembleai/tts";

const tts = new ResembleAITTSService({
  apiKey: process.env.RESEMBLE_API_KEY ?? "",
  // Resemble's WebSocket reference lists the project as required.
  projectUuid: process.env.RESEMBLE_PROJECT_UUID ?? null,
  settings: new ResembleAITTSService.Settings({ voice: "your-voice-uuid" }),
});
```

### Event handlers [#event-handlers]

| Event                 | Description              |
| --------------------- | ------------------------ |
| `on_connected`        | The WebSocket connected. |
| `on_disconnected`     | The WebSocket closed.    |
| `on_connection_error` | The connection failed.   |

## Notes [#notes]

* The sample rate defaults to 22050 Hz (8000, 16000, 22050, 32000 and 44100 work), `precision` to `PCM_16` and `outputFormat` to `wav`. Audio is requested without a WAV header.
* Word timestamps come from Resemble's per-character timings, so each pushed "word" is one character.
* A 401 or 403 error from Resemble closes the connection and opens a new one.
* Resemble doesn't acknowledge the WebSocket closing handshake, so the service doesn't wait for one.
* `projectUuid` is not an upstream option. Resemble's reference lists `project_uuid` as required, but upstream never sends it, so the service sends it only when you set it.

## Runtime notes [#runtime-notes]

* The WebSocket opens through the core `websocketConnect`, with the key in an `Authorization` header (through `fetch` on Cloudflare Workers), so it works on Bun, Node, Deno and Cloudflare Workers.
* The deprecated `voiceId` option is not ported. Use `settings`.
* Tested against a local WebSocket server, not against Resemble AI itself.

| Runtime            | Works | What it needs |
| ------------------ | ----- | ------------- |
| Bun                | ✅ yes | Nothing.      |
| Node.js            | ✅ yes | Nothing.      |
| Deno               | ✅ yes | Nothing.      |
| Cloudflare Workers | ✅ yes | Nothing.      |

Generated from `pipecat.runtimes` and `pipecat.compat` in `packages/resembleai/package.json`: ✅ means the compat smoke test passes on that runtime.