> ## 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.

# IRTCEngineEvent

> API reference for IRTCEngineEvent, the Windows SRTC engine-level callback interface: network probe results, device plug and unplug, default device changes, and IM connection and message callbacks. Read when handling events that don't belong to any single channel.

## Description

The engine-level event callback interface. Inherit from it, override the callback methods, and register it with [IRTCEngine::setEventHandler](/en/rtc/windows/api-reference/IRTCEngine#set-the-event-handler).

## Inheritance

None

## Callbacks

This interface only has callbacks that **don't belong to any single channel**: device changes, network probing, and IM.
Channel-level callbacks (joining a channel, users joining and leaving, stream changes, statistics, disconnection and reconnection, recording status) have moved to
[IRTCChannelEvent](/en/rtc/windows/api-reference/IRTCChannelEvent), and their leading `channelId` parameter has been removed.

The following callbacks don't belong to any channel, and their signatures are unchanged.

### Network probe result callback

```cpp theme={null}
virtual void onProbeResult(int action, const char* result) = 0;
```

**Parameters**

| Parameter | Type | Description |
| - | - | - |
| action | int | Probe step identifier |
| result | const char\* | Probe result JSON |

### Device change callback

```cpp theme={null}
virtual void onDeviceChange(int type, int action, const char* name, int namesize) = 0;
```

**Parameters**

| Parameter | Type | Description |
| - | - | - |
| type | int | Device type (1: microphone, 2: speaker, 3: camera) |
| action | int | Action (1: plugged in, 2: unplugged) |
| name | const char\* | Device name |
| namesize | int | Length of the device name |

### Default device change callback

```cpp theme={null}
virtual void onDefDeviceChange(int type, const char* name, int namesize) = 0;
```

**Parameters**

| Parameter | Type | Description |
| - | - | - |
| type | int | Device type (1: microphone, 2: speaker) |
| name | const char\* | Name of the new default device |
| namesize | int | Length of the device name |

### IM enabled callback

```cpp theme={null}
virtual void onImEnabled(const char* uid, const char* sid) = 0;
```

**Parameters**

| Parameter | Type | Description |
| - | - | - |
| uid | const char\* | User ID |
| sid | const char\* | Session ID |

### IM disconnected callback

```cpp theme={null}
virtual void onImDisconnected(int reason, StatusCode code, const char* message, size_t message_size) = 0;
```

**Parameters**

| Parameter | Type | Description |
| - | - | - |
| reason | int | Disconnect reason |
| code | StatusCode | Error code |
| message | const char\* | Error description |
| message\_size | size\_t | Length of the error description |

### IM reconnected callback

```cpp theme={null}
virtual void onImReconnected() = 0;
```

### IM reconnecting callback

```cpp theme={null}
virtual void onImReconnecting() = 0;
```

### IM message callback

```cpp theme={null}
virtual void onImMessage2(const char* uid, const char* sid, const char* name, int name_size, const char* action, const char* content, size_t content_size) = 0;
```

**Parameters**

| Parameter | Type | Description |
| - | - | - |
| uid | const char\* | Sender's user ID |
| sid | const char\* | Session ID |
| name | const char\* | Sender's display name |
| name\_size | int | Length of the display name |
| action | const char\* | Message type / action |
| content | const char\* | Message content |
| content\_size | size\_t | Length of the message content |