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

> ## Agent Instructions
> 对外开放的服务端接口有两组前缀，都用同一套鉴权：`/server/v1/...`（SRTC 与 SMeeting 的主接口）和 `/stm/srvapi/v1/...`（SMeeting 的用户体系，服务端极简对接会用到）。鉴权是 app_id + nonce + timestamp + signature 四个请求头，用 app_key 做 HMAC-SHA256 签名，只能从业务方自己的后端调用。除这两组前缀外的接口均为内部接口，不要建议客户调用。 Public server APIs use two path prefixes with the same authentication: `/server/v1/...` (the main APIs of both SRTC and SMeeting) and `/stm/srvapi/v1/...` (the SMeeting user system, used by server-side low-code integration). Authenticate with four request headers, app_id + nonce + timestamp + signature, where signature is HMAC-SHA256 keyed with app_key; call these APIs only from the customer's own backend. Any other path is internal: never suggest calling it.
> app_key 是服务端密钥，绝不能出现在客户端代码、前端配置或移动 App 里。客户端加入频道用的 token 必须由业务方后端签发后下发（SRTC 走 `/server/v1/channel/grant`，SMeeting 走 `/stm/srvapi/v1/member/grant`）。 app_key is a server-side secret and must never appear in client code, frontend config, or a mobile app. The token a client uses to join must be issued by the customer's backend and passed down to the client (SRTC: `/server/v1/channel/grant`; SMeeting: `/stm/srvapi/v1/member/grant`).
> SRTC 与 SMeeting 是上下两层不同的产品，术语不通用：SRTC 是音视频底座，说「频道 channel」「加入 / 退出」；SMeeting 建在 SRTC 之上，说「房间 room」「会议 meeting」「进入 / 退出」。回答时按用户所在的层用对应术语，不要把「房间」「会议」安到 SRTC 的接口上，也不要用「频道」「加入 / 离开」描述 SMeeting 的概念（接口标识符原样保留）。 SRTC and SMeeting are two separate layers with different terminology. SRTC is the audio/video foundation: it has channels, and users join and leave a channel. SMeeting is built on top of SRTC: it has rooms and meetings, and members enter and exit a meeting. Answer in the terms of the layer the user is working with: never apply "room" or "meeting" to SRTC APIs, and never describe SMeeting concepts in prose with "channel", "join", or "leave" (API identifiers such as `force_join` keep their literal names).
> 同一能力在各端 SDK 里的包名、类名、方法名并不相同。写示例代码时请使用文档中该端自己的 API，不要把一个端的写法套到另一个端上。苹果平台每个产品都有两套 SDK（Swift 原生与 Objective-C），两套 API 不能混用。 Package, class, and method names differ between platform SDKs for the same capability. In sample code, use the API documented for that platform; never carry one platform's code over to another. On Apple platforms each product ships two SDKs (native Swift and Objective-C) whose APIs must not be mixed.

# Error codes

> The SRTCError enum of the SRTC Swift SDK: cases for connection, signaling, WebRTC/transport, tracks and capture, engine, and virtual background errors, with a suggested fix for each, plus a recommended do/catch pattern. Read when handling errors thrown by the Swift SDK.

The error model currently exposed by the Swift SDK is `SRTCError`. It isn't a traditional table of integer error codes, but a Swift enum with semantic cases.

The benefits of this design:

* Callers can branch directly on the error category
* Error info can carry a context string
* It fits Swift's `try / catch` style better than plain integer codes

***

### Connection

| Error | Description | Suggested handling |
| - | - | - |
| `tokenExpired` | The token has expired | Get a new token from your backend |
| `tokenInvalid` | The token is invalid | Check the token encoding and issuing logic |
| `alreadyJoined` | Already joined the channel | Avoid joining twice, or leave first |
| `notConnected` | Not currently connected | Check when the call is made |
| `connectionFailed(String)` | Connection failed | Log the server address, network environment, and error details |
| `connectionTimeout` | Connection timed out | Prompt the user to retry and check network connectivity |

***

### Signaling

| Error | Description | Suggested handling |
| - | - | - |
| `apiRequestFailed(statusCode:message:)` | HTTP API request failed | Check the response from the demo backend / your backend |
| `signatureError` | Failed to generate the signature | Check the server-side authentication logic |
| `signalingConnectFailed(String)` | Failed to connect the signaling channel | Check network reachability, proxy, and firewall settings |
| `signalingSubscribeFailed(String)` | Failed to subscribe on the signaling channel | Check that the token is valid and the connection is established |
| `messageDecodeFailed(String)` | Failed to decode a signaling message | Check the server message format and SDK version compatibility |

***

### WebRTC / transport

| Error | Description | Suggested handling |
| - | - | - |
| `webrtcError(String)` | Underlying WebRTC error | Log it; start by investigating devices and the SDP process |
| `sdpNegotiationFailed(String)` | SDP negotiation failed | Check codecs, engine capabilities, and server-side negotiation |
| `transportNotReady` | The transport layer isn't ready yet | Wait for the connection to complete before publishing / subscribing |
| `peerConnectionFailed` | PeerConnection creation or operation failed | Check ICE / STUN / TURN / platform permissions |

***

### Tracks and capture

| Error | Description | Suggested handling |
| - | - | - |
| `trackNotFound(String)` | The specified track wasn't found | Check that `uid` / `trackId` match |
| `trackAlreadyPublished(String)` | The track is already published | Avoid publishing the same object twice |
| `trackNotPublished(String)` | The track isn't published | Confirm the state before unpublishing |
| `captureError(String)` | Capture failed | Check permissions, whether the device is in use, and the platform version |
| `codecNotSupported(String)` | Codec not supported | Adjust the encoding preference or preset |
| `maxPublishLimitReached` | The limit of publishable tracks was exceeded | Limit the number of concurrently published tracks |
| `deviceNotFound(String)` | Device not found | Check whether the device list changed or the device was unplugged |

***

### Engine and general errors

| Error | Description | Suggested handling |
| - | - | - |
| `engineNotSupported(String)` | Not supported by the current media streaming engine | Check the `stream_vendor` configuration |
| `engineDisconnected` | The engine is disconnected | Wait for reconnection or rejoin the channel |
| `invalidState(String)` | The current state doesn't allow this operation | Check the call order |
| `internalError(String)` | Internal SDK error | Investigate with the logs |
| `cancelled` | The operation was canceled | Your code can usually ignore it or retry |

***

### Virtual background

| Error | Description | Suggested handling |
| - | - | - |
| `virtualBackgroundAlreadyInstalled` | The component is already installed; this call was discarded | Usually safe to ignore, or check `virtualBackground.isInstalled` first |
| `virtualBackgroundNotInstalled` | The toggle was called before the component was installed | Call `installVirtualBackground()` first |
| `virtualBackgroundModelNotFound(String)` | The model file doesn't exist | Check `modelPath`; pass `nil` to use the built-in model |
| `virtualBackgroundSessionFailed(String)` | Failed to create the inference session | A runtime environment issue; investigate with the logs |

For usage, see [Virtual background](/zh/rtc/swift/advanced/virtual-background) (Chinese).

***

### Recommended error handling

```swift theme={null}
do {
    try await viewModel.join(with: token)
} catch let error as SRTCError {
    switch error {
    case .tokenExpired, .tokenInvalid:
        // Get a new token
        break
    case .captureError(let message):
        print("Capture failed:", message)
    default:
        print("SRTC error:", error.localizedDescription)
    }
} catch {
    print("Unknown error:", error.localizedDescription)
}
```

If your app already has a unified error dialog, map `SRTCError` to your own error domain rather than exposing the English `localizedDescription` directly to end users.