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

# Backend Mode with your own transport

> Backend Mode Integration where your backend relays encoded audio payloads and motion data payloads directly to clients.

## What is Backend Mode with your own transport?

This is the [Backend Mode Integration](/backend-mode/overview) shape where **your application** owns the network connection between the Server SDK and the client. Your server sends encoded audio payloads and motion data payloads to your client, and the client SDK receives and **decodes them internally** for synchronized playback and rendering.

The Reference tab covers the exact enum and method names for each platform.

```mermaid theme={null}
flowchart LR
    A["Server SDK"] -->|encoded audio payloads + motion data payloads| B["Your App<br/>(Network Layer)"]
    B -->|yieldAudioData| C["AvatarKit<br/>Client SDK"]
    B -->|yieldFramesData| C
    C -->|Decode & Render| D["🖥️ Avatar Rendering"]
```

<Warning>
  Backend Mode with your own transport **requires** the Server SDK to provide the encoded payloads. The data passed to `yieldAudioData()` and `yieldFramesData()` are encoded audio payloads and motion data payloads from the Server SDK — not raw audio or motion data you create yourself.
</Warning>

## When to use

* **Custom network layer** — you manage the connection between your client and AvatarKit's server SDK yourself.
* **Third-party realtime transport** — messages are relayed through a provider such as LiveKit. (See [Backend Mode with LiveKit](/backend-mode/with-livekit) for that variant.)
* **Proxy architecture** — your backend acts as a relay between the client and Motion Server.

## Requirements

| Requirement       | Description                                                                      |
| ----------------- | -------------------------------------------------------------------------------- |
| **App ID**        | Obtained from [Spatius Studio](https://app.spatius.ai).                          |
| **Session Token** | **Not required** on the client side.                                             |
| **Server SDK**    | Your backend must integrate with the Server SDK to provide payloads for clients. |

## Direct Mode vs Backend Mode (own transport)

| Aspect               | Direct Mode                                    | Backend Mode (own transport)                  |
| -------------------- | ---------------------------------------------- | --------------------------------------------- |
| **Network**          | Client SDK connects to Motion Server directly. | Your app relays payloads from the Server SDK. |
| **Message decoding** | Handled internally.                            | Handled internally (same).                    |
| **Session Token**    | Required (client-side).                        | Not required (client-side).                   |
| **Server SDK**       | Not needed.                                    | **Required** on your backend.                 |
| **Key methods**      | `send()`, `start()`, `close()`                 | `yieldAudioData()`, `yieldFramesData()`       |

## Key Concepts

### ConversationId Management

ConversationId links encoded audio payloads and motion data payloads for a single conversation session:

1. Call `yieldAudioData()` — returns a `conversationId`.
2. Use that `conversationId` when calling `yieldFramesData()`.
3. Messages with a **mismatched** conversationId will be **discarded**.

<Warning>
  **Important:** Always use the conversationId returned by `yieldAudioData()` when sending motion data payloads. Mismatched IDs cause payloads to be silently dropped.
</Warning>

### Fallback Mechanism

If you provide empty motion data (empty array or undefined), the SDK automatically enters **audio-only mode** for that session. Once in audio-only mode, any subsequent motion data for that session is ignored — only audio continues playing.

## Next steps

<CardGroup cols={2}>
  <Card title="Browse all demos" icon="github" href="/resources/demo-projects">
    Run the Backend Mode reference implementations for Web, iOS, Android, and Flutter.
  </Card>

  <Card title="Backend Mode with LiveKit" icon="tower-broadcast" href="/backend-mode/with-livekit">
    Reuse a LiveKit room as the downstream transport instead of your own WebSocket.
  </Card>
</CardGroup>