> ## 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.

# RTCChannel

> API reference for RTCChannel, the Android handle for a single channel returned by RTCEngine.join(...): lifecycle, listeners, user and track queries, publishing, subscription, ASR, and media statistics, all isolated per channel. Read when working with multiple channels or per-channel operations.

`RTCChannel` is returned by `RTCEngine.join(...)`, and all of its methods act only on the channel session bound to that handle. The first `join` returns the default channel handle; the flat channel APIs retained on `RTCEngine` operate on the same session as this handle.

A non-null handle only means the SDK accepted the join request. Call publishing, subscription, and info queries after `RTCClientEvent.onJoinSucceed(...)`.

## Identity and lifecycle

### channelId

```kotlin theme={null}
val channelId: String?
```

The channel ID. If the token can be parsed, it may be available before the join succeeds; otherwise it's filled in by the success callback. Don't treat a non-null value as a successful join.

### leave()

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

Leaves and tears down the current channel without affecting other channels or shared capture devices.

### resume()

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

Immediately triggers a heartbeat check for the current channel after the app resumes from a state such as screen-off.

## Listeners

```kotlin theme={null}
fun setRtcClientEvent(e: RTCClientEvent?)
fun setRtcMediaEvent(e: RTCMediaEvent?)
```

* `setRtcClientEvent`: replaces or unbinds the channel control listener after the join succeeds. The initial listener must be passed to `join(...)`.
* `setRtcMediaEvent`: replaces or unbinds the media listener for the current channel; you can set it after `join(...)` returns the handle.

## Channel, user, and track queries

```kotlin theme={null}
fun getChannelInfo(): ChannelInfo?
fun getMeInfo(): UserInfo?
fun isAudience(): Boolean
fun getUserInfos(): MutableList<UserInfo>
fun getUserInfo(uid: String): UserInfo?
fun getTrackInfos(uid: String): List<TrackInfo>
fun getTrackInfoByTrackDesc(uid: String, trackDesc: String): TrackInfo?
fun getTrackInfoByTrackId(uid: String, trackId: String): TrackInfo?
```

These queries read only the current channel's data. When not joined or the target doesn't exist, nullable methods return `null` and list methods return an empty list; `isAudience()` returns `false` when not joined.

## Publish local tracks

```kotlin theme={null}
fun publishLocalVideo(
    track: LocalVideoTrack,
    publishCustomOpt: PublishCustomOptions?,
    listener: RTCResultListener?
)

fun publishLocalAudio(
    track: LocalAudioTrack,
    publishCustomOpt: PublishCustomOptions?,
    listener: RTCResultListener?
)

fun unPublishLocalVideo(track: LocalVideoTrack, listener: RTCResultListener?)
fun unPublishLocalAudio(track: LocalAudioTrack, listener: RTCResultListener?)
fun enableLocalAudio(track: LocalAudioTrack, enable: Boolean): Boolean
```

Local tracks are created and shared by `RTCEngine`, but publishing state is isolated per channel. When an audience user calls a publishing API, it fails with `FORBIDDEN_FOR_AUDIENCE`. `enableLocalAudio` only toggles audio already published in the current channel with low latency; it doesn't close microphone capture or remove the remote track.

## Subscribe to remote tracks

```kotlin theme={null}
fun getRemoteVideoTrack(uid: String, trackDesc: String): RemoteVideoTrack?
fun getRemoteStreamTrack(uid: String, trackDesc: String): RemoteVideoTrack?
fun getRemoteMixtureTrack(): RemoteVideoTrack?
fun getRemoteAudioMixTrack(): RemoteAudioMixTrack?

fun subscribeRemoteTrack(
    uid: String,
    trackId: String,
    preferTrackIds: MutableList<String>?,
    result: RTCResultListener?
)
fun unSubscribeRemoteTrack(uid: String, trackId: String)

fun subscribeRemoteStream(
    streamName: String,
    uid: String,
    trackDesc: String,
    kind: String?,
    result: RTCResultListener?
)
fun unSubscribeRemoteStream(
    streamName: String,
    uid: String,
    trackDesc: String,
    kind: String?
)

fun subscribeRemoteMixture()
fun unSubscribeRemoteMixture()
```

Remote tracks, subscription IDs, and render objects must all come from the same channel. `getRemoteStreamTrack` and `subscribeRemoteStream` work only with the Wangsu media streaming engine; other engines return `STREAM_VENDOR_NOT_SUPPORTED` or an empty result.

## Statistics and ASR

```kotlin theme={null}
fun getMetric(): MediaMetric.Metric?
fun startAsr()
fun stopAsr()
fun isStartAsr(): Boolean
```

Each channel has its own media statistics and ASR state. `getMetric()` returns the most recent thread-safe snapshot and doesn't actively trigger underlying statistics collection.

For the full multi-channel integration flow, see [Multi-channel](/en/rtc/android/advanced/multi-channel).