> ## 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.

# MeetingMicDeviceEvent

> Receive changes to the process-wide shared mic input device list and invalidation of the current device through MeetingEngine.micDeviceEvent, before and during the meeting. Read this when you show a mic picker or handle unplugged devices.

`MeetingMicDeviceEvent` is an Engine-level mic device listener that isn't bound to a specific meeting, registered through `MeetingEngine.micDeviceEvent`. You can extend `MeetingMicDeviceSimpleEvent` and override only what you need.

## Usage notes

* This event covers changes to the process-wide shared audio input devices; the same listener is used before and during the meeting.

* Callbacks stay on the actual source thread of the device layer; switch to the main thread before updating the UI.

* After the current device becomes invalid, SRTC may fall back to another input automatically; your app should refresh the UI based on the subsequent device list.

## Methods

### onMicDeviceListChanged(devices)

```kotlin theme={null}
fun onMicDeviceListChanged(devices: List<MicDeviceCapability>)
```

Description: The full list of mic input devices available on the system changed.

Parameters:

| Parameter | Description |
| - | - |
| `devices` | The full device capability list after the change. |

Returns: None (`Unit`).

### onMicDeviceInvalid(deviceId, reason)

```kotlin theme={null}
fun onMicDeviceInvalid(deviceId: String, reason: String)
```

Description: The mic device used for current capture became invalid; SRTC falls back to an available input according to its own policy.

Parameters:

| Parameter | Description |
| - | - |
| `deviceId` | ID of the device that became invalid. |
| `reason` | Invalidation reason provided by the underlying layer. |

Returns: None (`Unit`).