External conversation engine

When to use

You want full control over the speech stack — STT, LLM, TTS, turn detection, tools, memory — and run it yourself.
You already have a Pipecat, LiveKit Agents, custom Python/Node, or other voice agent and need to give it a face.
The hosted engines (OpenAI Realtime, Cartesia) don’t fit your pipeline.

A reference implementation (Pipecat + Pipecat Cloud, OpenAI Realtime or cascaded STT/LLM/TTS) lives at github.com/avaturn-live/pipecat-avaturn-live-demo.

How it works

When you create a session with type: "external", Avaturn opens a WebSocket to the url you provide and exchanges:

Binary — raw PCM16LE mono audio in both directions.
JSON — small control protocol that frames every burst of avatar speech as a segment and propagates playback events back to your engine.

Your engine owns the conversation; Avaturn owns the avatar’s mouth, eyes, and playback clock.

Prerequisites

A reachable WebSocket endpoint — wss:// in production. Avaturn must reach it over the public internet.
Avaturn API key (dashboard).
A way to authenticate the incoming WebSocket (shared secret, signed token, IP allowlist — your choice; see Authentication).

1. Create the Avaturn session

import httpx

async with httpx.AsyncClient() as http:
    r = await http.post(
        "https://api.avaturn.live/api/v1/sessions",
        headers={"Authorization": "Bearer <AVATURN_API_KEY>"},
        json={
            "conversation_engine": {
                "type": "external",
                "url": "wss://your-engine.example.com/avaturn-live/ws",
                "audio": {"user": {"sample_rate": 24000}},
                "headers": {"Authorization": "Bearer <YOUR_SHARED_SECRET>"},
            },
        },
    )
    r.raise_for_status()
    session = r.json()  # { "session_id": "...", "token": "..." }

const r = await fetch("https://api.avaturn.live/api/v1/sessions", {
  method: "POST",
  headers: {
    Authorization: "Bearer <AVATURN_API_KEY>",
    "Content-Type": "application/json",
  },
  body: JSON.stringify({
    conversation_engine: {
      type: "external",
      url: "wss://your-engine.example.com/avaturn-live/ws",
      audio: { user: { sample_rate: 24000 } },
      headers: { Authorization: "Bearer <YOUR_SHARED_SECRET>" },
    },
  }),
});
const session = await r.json(); // { session_id, token }

curl -X POST https://api.avaturn.live/api/v1/sessions \
  -H "Authorization: Bearer <AVATURN_API_KEY>" \
  -H "Content-Type: application/json" \
  -d '{
    "conversation_engine": {
      "type": "external",
      "url": "wss://your-engine.example.com/avaturn-live/ws",
      "audio": { "user": { "sample_rate": 24000 } },
      "headers": { "Authorization": "Bearer <YOUR_SHARED_SECRET>" }
    }
  }'

conversation_engine fields:

Field	Type	Notes
`type`	`"external"`	Required.
`url`	string	`wss://` URL Avaturn opens. Must be reachable from Avaturn’s infra.
`audio.user.sample_rate`	`16000` \| `24000`	Sample rate of the user-mic stream Avaturn sends you. Default `24000`. Use `24000` for speech-to-speech LLMs that consume audio natively (OpenAI Realtime, Gemini Live). Pick `16000` if you’d rather halve the upstream bitrate — most VAD and turn-detection models (Silero, Smart Turn) work at 16 kHz internally.
`headers`	`Record<string,string>` \| `null`	Optional. Forwarded on the WebSocket upgrade — typically `Authorization: Bearer ...`. The values are stored only for the lifetime of the session.

Optional top-level session fields: avatar_id, background, model (render model, default delta), user_absent_timeout (default 60s, min 10), max_duration (default 3600s, min 60s, max 86400s). See the API reference. Response:

session_id — backend handle
token — short-lived credential for the Web SDK

2. Connect from the frontend

import { AvaturnHead } from "@avaturn-live/web-sdk";

// Trigger the mic permission prompt inside the click handler — the SDK
// otherwise calls getUserMedia outside a user gesture and silently fails
// on some browsers.
const stream = await navigator.mediaDevices.getUserMedia({ audio: true });
stream.getTracks().forEach((t) => t.stop());

const root = document.querySelector<HTMLDivElement>("#avaturn-video")!;
const avatar = new AvaturnHead(root, {
  sessionToken: session.token,
  audioSource: true, // required — engine is voice-to-voice
});

await avatar.init();

3. Implement the WebSocket protocol

Once the session is created, Avaturn opens a WebSocket to your url (with your headers) and starts streaming the user’s microphone immediately.

Audio

Direction	Format
Avaturn → engine	Binary PCM16LE mono @ `audio.user.sample_rate`
Engine → Avaturn	Binary PCM16LE mono @ 24 kHz (avatar speech)

Resample your TTS output to 24 kHz mono before sending it. Anything else will play back garbled. If your TTS supports native 24 kHz mono output, prefer that over resampling — fewer artifacts and one less CPU step in the hot path. Chunk size is up to you. 10–40 ms per binary frame works well in practice; Avaturn buffers per segment, so chunk size only affects time-to-first-frame, not playback quality. Don’t throttle output to real-time. Avaturn Live owns the playback clock and pulls audio as fast as you can produce it — if your framework paces writes by default (some WebSocket transports do), disable that pacing for this socket or segment timing will drift.

Control messages (engine → Avaturn)

Every chunk of avatar audio must live inside an open segment. Open one with segment.create before pushing any bytes, then segment.close after the last chunk.

{ "type": "avatar.speech.segment.create", "segment_uid": "<your-id>" }
{ "type": "avatar.speech.segment.close",  "segment_uid": "<your-id>" }
{ "type": "avatar.speech.interrupt" }
{ "type": "sdk.message.send", "data": { /* opaque object */ } }

segment_uid is your own correlation id (any string). Avaturn echoes it back on the corresponding playback events so you can match them up.
avatar.speech.interrupt discards anything Avaturn has buffered for playback. Use it when your turn detector decides the user has barged in.
sdk.message.send forwards an arbitrary JSON payload to the Web SDK over the data channel (see Web SDK events).

Audio sent outside an open segment is dropped and Avaturn replies with an error frame — open the segment first.

Control messages (Avaturn → engine)

{ "type": "avatar.speech.segment.created",   "segment_id": "...", "segment_uid": "..." }
{ "type": "avatar.speech.segment.closed",    "segment_id": "...", "segment_uid": "..." }
{ "type": "avatar.speech.segment.playback.started",     "segment_id": "...", "segment_uid": "...", "timestamp": 0.42 }
{ "type": "avatar.speech.segment.playback.ended",       "segment_id": "...", "segment_uid": "...", "timestamp": 3.18 }
{ "type": "avatar.speech.segment.playback.interrupted", "segment_id": "...", "segment_uid": "...", "played_duration": 1.07 }
{ "type": "sdk.message.receive", "data": { /* opaque object */ } }
{ "type": "error", "subtype": "...", "reason": "..." }

segment_id is Avaturn’s id; segment_uid is the one you supplied. Use whichever is convenient.
playback.started / playback.ended fire when the avatar actually starts/finishes lip-syncing the segment — useful for transcript timing.
playback.interrupted fires after avatar.speech.interrupt or when a new user utterance pre-empts the current segment.
sdk.message.receive carries messages sent from the browser via the Web SDK.

error frames are advisory — the WebSocket stays open. Most common subtypes:

`subtype`	Fires when
`avatar.speech.segment.error`	You pushed audio bytes outside an open segment, or tried to `create` while another was still open. Open / close the segment as expected and retry.
`message.type.error`	An incoming JSON frame had an unknown `type`. Check spelling against the outgoing-message list.
`json.parsing.error`	An incoming text frame wasn’t valid JSON.

Segment lifecycle

A correct turn looks like: Only one segment can be open at a time. Attempting to create while another is open returns an error — close the current one first.

Authentication

Anything reachable on the public internet at a guessable URL is a free avatar — set up auth before exposing the endpoint.

Shared secret in headers. Pass {"Authorization": "Bearer <secret>"} when creating the session and check it in your WS upgrade handler. Simple and good enough for most deployments.
Per-session signed token in the URL path. Mint a short-lived HMAC token at session-create time and bake it into the url (e.g. wss://engine.example.com/ws/<token>). The token is single-use and self-expiring, so the secret never leaves your infra. This is the pattern the reference demo uses for Pipecat Cloud.
IP allowlist. Contact support@avaturn.me for the current egress range if you want network-level filtering in front of your service.

Connection behavior

Keep-alive. Avaturn sends WebSocket pings every ~75 seconds with a 30-second pong timeout. Most reverse proxies need an idle-timeout ≥ 180 seconds in front of your engine to avoid mid-conversation drops — bump proxy_read_timeout (nginx), idle timeout (ALB, Cloudflare), or the equivalent. You don’t need to send application-level pings yourself; Avaturn’s WebSocket-protocol pings are sufficient.
Disconnect = session end. If your engine closes the socket, the Avaturn session ends. If Avaturn closes it (e.g. user disconnected, max_duration reached), recv() returns end-of-stream — drain and exit cleanly.
No automatic reconnect. Avaturn does not retry failed upgrades or dropped connections inside an active session. Make sure your engine is up before the session starts.

Session lifecycle

A session ends on any of:

Explicit DELETE /api/v1/sessions/{session_id}
The conversation-engine WebSocket closing
user_absent_timeout elapses with the user disconnected (default 60s)
max_duration cap reached (default 3600s, max 86400s)

async with httpx.AsyncClient() as http:
    await http.delete(
        f"https://api.avaturn.live/api/v1/sessions/{session_id}",
        headers={"Authorization": "Bearer <AVATURN_API_KEY>"},
    )

Call avatar.dispose() on the frontend to tear down the local SDK state. The backend session terminates as described above — dispose() does not directly close it.

Reference implementation

github.com/avaturn-live/pipecat-avaturn-live-demo — a full open-source reference. Two pipelines ship side-by-side, switchable via a single env var: speech-to-speech (OpenAI Realtime) and cascaded (STT → LLM → TTS). Same transport, serializer, and segment processor wrap both.

pipecat_avaturn/serializer.py — bidirectional Pipecat ↔ Avaturn wire format. Read this first to see the protocol on the wire.
pipecat_avaturn/segment_processor.py — TTSStartedFrame / TTSStoppedFrame → segment.create / segment.close.
pipecat_avaturn/transport.py — the Pipecat FastAPI WebSocket transport with its default real-time pacing sleep disabled. The non-obvious gotcha for anyone building a streaming engine — see the “Don’t throttle output” note in Audio.
pipecat_avaturn/broker.py — minimal client for POST /api/v1/sessions with type: "external".
server.py — FastAPI app combining the session broker and the conversation engine in one process.

Fork it, swap in your own STT/LLM/TTS, and you have a production-shaped Avaturn integration in an afternoon.

Get Started

Conversation Engines

Web SDK

REST API

Legacy

External conversation engine

When to use

How it works

Prerequisites

1. Create the Avaturn session

2. Connect from the frontend

3. Implement the WebSocket protocol

Audio

Control messages (engine → Avaturn)

Control messages (Avaturn → engine)

Segment lifecycle

Authentication

Connection behavior

Session lifecycle

Reference implementation

See also

​When to use

​How it works

​Prerequisites

​1. Create the Avaturn session

​2. Connect from the frontend

​3. Implement the WebSocket protocol

​Audio

​Control messages (engine → Avaturn)

​Control messages (Avaturn → engine)

​Segment lifecycle

​Authentication

​Connection behavior

​Session lifecycle

​Reference implementation

​See also

When to use

How it works

Prerequisites

1. Create the Avaturn session

2. Connect from the frontend

3. Implement the WebSocket protocol

Audio

Control messages (engine → Avaturn)

Control messages (Avaturn → engine)

Segment lifecycle

Authentication

Connection behavior

Session lifecycle

Reference implementation

See also