> ## 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.

# LocalMicTrack

> Android shared microphone capture track: explicitly start and stop capture independently of any channel, read the volume, enumerate and switch input devices, receive local PCM, and publish to one or more channels. Read when working with microphone audio on Android.

`LocalMicTrack` is created by `RTCEngine.getLocalMicTrack(...)`. Microphone capture is decoupled from joining a channel and publishing audio: the app must explicitly call `startCapture(...)` to open the shared microphone, then publish through `RTCEngine` or `RTCChannel.publishLocalAudio(...)`.

The same `LocalMicTrack` can be published to multiple channels. Unpublishing from one channel doesn't stop capture; `stopCapture()` closes the shared data source and affects every channel still using the track.

## startCapture(listener)

```kotlin theme={null}
fun startCapture(listener: RTCResultListener?)
```

Opens microphone capture. Repeated calls with the same parameters are idempotent. After it succeeds, you can read the volume, receive local PCM callbacks, or publish to a channel.

| Parameter | Type | Description |
| - | - | - |
| `listener` | `RTCResultListener?` | The start result; can be `null`. For failure codes, see [Error codes](/en/rtc/android/error-codes). |

## stopCapture()

```kotlin theme={null}
fun stopCapture()
```

Closes shared microphone capture. Calling it when capture hasn't started is idempotent.

## getVolume()

```kotlin theme={null}
fun getVolume(): Int
```

Returns the real-time microphone volume in dBFS, roughly in the range `[-60, 0]`; returns the implementation's silence value when not capturing.

## switchMicDevice(deviceId)

```kotlin theme={null}
fun switchMicDevice(deviceId: String)
```

Switches the microphone input device. `deviceId` comes from `getMicDevices()` and is valid only while the device stays connected; switching during capture rebuilds the recording pipeline.

## getMicDevices()

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

Returns the capabilities of the microphone input devices currently available on the system. For fields, see [Types](/en/rtc/android/types). `getMicDevices()` and `switchMicDevice(...)` on the Engine are convenience entry points to the same shared capture module.

## Local PCM callback

```kotlin theme={null}
rtcEngine.setRtcLocalAudioFrameEvent(object : RTCLocalAudioFrameEvent {
    override fun onLocalAudioFrame(
        pcm: ByteArray?,
        sampleRate: Int,
        channelCount: Int,
        audioFormat: Int
    ) {
        // Don't perform time-consuming I/O on the callback thread
    }
})

val micTrack = rtcEngine.getLocalMicTrack(PreOptionMic.def)
micTrack.startCapture(listener)
```

Registering the frame listener alone doesn't open the microphone. For full parameters, see [RTCLocalAudioFrameEvent](/en/rtc/android/api-reference/RTCLocalAudioFrameEvent).