> ## 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.

# RTCLocalAudioFrameEvent

> Android callback that delivers local PCM frames from shared microphone capture, for local recording, writing to disk, or app-level audio processing: parameters, threading, and the requirement to start LocalMicTrack capture. Read when you need raw local microphone audio on Android.

Register the local PCM callback with `RTCEngine.setRtcLocalAudioFrameEvent(...)`; pass `null` to unbind. The callback belongs to the Engine's shared capture layer and carries no channel ID; in multi-channel scenarios, each physically captured frame is delivered only once, and the SDK's own publishing doesn't depend on this listener.

## onLocalAudioFrame(pcm, sampleRate, channelCount, audioFormat)

```kotlin theme={null}
fun onLocalAudioFrame(
    pcm: ByteArray?,
    sampleRate: Int,
    channelCount: Int,
    audioFormat: Int
)
```

| Parameter | Type | Description |
| - | - | - |
| `pcm` | `ByteArray?` | PCM data copied by the SDK for the app, usually 16-bit little-endian. |
| `sampleRate` | `Int` | Sample rate in Hz, for example `48000`. |
| `channelCount` | `Int` | Number of audio channels; `1` is mono, `2` is stereo. |
| `audioFormat` | `Int` | Sample format, consistent with `android.media.AudioFormat.ENCODING_*`. |

:::warning
Registering the listener doesn't open the microphone by itself. You must call `LocalMicTrack.startCapture(...)`; PCM callbacks start only after it succeeds, and stop after you call `stopCapture()`.

Callbacks run serially on the SDK's audio dispatch thread and aren't guaranteed to be on the main thread. The PCM is a separate copy for the app, so modifying it doesn't affect the SDK's uplink, and time-consuming processing doesn't block the uplink either; however, when the side queue stays full, older app callback frames are dropped first. For recording or writing to disk, still hand frames off quickly to your app's own work queue.
:::

```kotlin theme={null}
rtcEngine.setRtcLocalAudioFrameEvent(object : RTCLocalAudioFrameEvent {
    override fun onLocalAudioFrame(
        pcm: ByteArray?,
        sampleRate: Int,
        channelCount: Int,
        audioFormat: Int
    ) {
        // Hand off quickly to the app's own recording or processing queue
    }
})

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