> ## 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.

# Camera presets

> The PreOptionCamera camera preset of the SMeeting Android SDK, the capture + publish structure (CameraCaptureOptions, VideoPublishOptions) shared by all presets, the known minBitrate limitation, and built-in 1080P/720P/480P/180P values. Read this when choosing camera resolution and bitrate.

This page describes the camera preset `PreOptionCamera` and defines the "capture configuration + publish configuration" structure shared by all presets. The mic, screen sharing, and custom video presets all reuse this page's `VideoPublishOptions` for their publish parameters.

## General notes

Purpose: `PreOption*` presets all use a "capture configuration + publish configuration" structure.

* Capture configuration: controls local capture behavior (resolution, frame rate, sample rate, device parameters, etc.).
* Publish configuration: controls publish behavior (`desc`, `codec`, `maxBitrate`, simulcast parameters, etc.).

In meetings, the camera preset is passed through `openCamera` / `openCameraAndPublish`, the mic preset through `openMic` / `openMicAndPublish`, and the screen sharing preset through `initScreenShare`. When `null` is passed for the camera, the default preset is used the first time, and the existing Track configuration is reused after that.

## PreOptionCamera

Purpose: Camera track preset that combines camera capture parameters and video publish parameters.

### Structure

`PreOptionCamera(capture: CameraCaptureOptions, publish: VideoPublishOptions)`

| Property | Type | Description |
| - | - | - |
| capture | `CameraCaptureOptions` | Camera capture configuration |
| publish | `VideoPublishOptions` | Camera video publish configuration |

### Capture configuration CameraCaptureOptions

Purpose: Configures camera capture parameters.

| Property | Type | Description |
| - | - | - |
| deviceId | `String` | Suggested device ID; the default empty string means none is specified. If it's unavailable at startup, the SDK automatically picks another device with the same facing first, then from all devices. |
| position | `CamraPosition` | Phone camera position: `FRONT` / `BACK` / `External`. |
| facingMode | `CameraFacingMode` | WebRTC facing: `USER` / `ENVIRONMENT` / `LEFT` / `RIGHT`. |
| width | `Int` | Capture width. |
| height | `Int` | Capture height. |
| maxFps | `Int` | Maximum capture frame rate. |

### Publish configuration VideoPublishOptions

Purpose: Configures video track publish parameters. All video presets other than the mic reuse this structure.

| Property | Type | Description |
| - | - | - |
| desc | `String` | Track description (the high stream usually uses `TRACK_MAIN`, the low stream usually uses `TRACK_SUB`). |
| codec | `CodecType` | Codec (usually `H264`). |
| maxBitrate | `Int` | Maximum bitrate per stream in bps; set before publishing. |
| minBitrate | `Int?` | Minimum bitrate per stream (bps); `null` uses the engine's default lower bound. A non-null value should satisfy `0 <= minBitrate <= maxBitrate`. Each stream is configured independently and set before publishing; currently only supported by the SFU. |
| width | `Int` | Publish width. |
| height | `Int` | Publish height. |
| maxFps | `Int` | Maximum publish frame rate. |
| props | `Any?` | Custom properties. |
| simulcasts | `MutableList<VideoPublishOptions>?` | Simulcast / low stream configuration (currently one low stream can be configured for the camera). |

### Known minBitrate limitation

RTC `2.0.33` to `2.0.35` still have this limitation: `VideoPublishOptions.deepCopy()` doesn't copy `minBitrate`, so after copying, `minBitrate` becomes `null` for both the high and low streams. Meeting's parameter parsing and the RTC publish pipeline use deep copies, so the minimum bitrates in the table below are the values declared by the presets—you can't conclude from them that these versions actually publish with these lower bounds. This issue needs to be fixed and released in RTC before it can be verified; setting the field only on the app side can't get around the later deep copy.

### Built-in presets

Purpose: The following built-in values take effect from RTC `2.0.33` (introduced with Meeting `2.0.37`). Capture and publish frame rates are uniformly 15, an intentional adjustment in RTC; if you need another frame rate, pass it explicitly from your app. A new preset doesn't take effect while capture is already running; close and reopen the camera first.

The following presets are supported: `_1080P`, `_720P`, `_480P`, `_180P`.

```kotlin theme={null}
// _1080P
capture: deviceId="", position=FRONT, facingMode=USER, width=1920, height=1080, maxFps=15
publish(main): desc="camera_big"(TRACK_MAIN), codec=H264, maxBitrate=5000*1024, minBitrate=2500*1024, width=1920, height=1080, maxFps=15
publish(sub):  desc="camera_small"(TRACK_SUB), codec=H264, maxBitrate=160*1024, minBitrate=80*1024, width=320, height=180, maxFps=15

// _720P
capture: deviceId="", position=FRONT, facingMode=USER, width=1280, height=720, maxFps=15
publish(main): desc="camera_big"(TRACK_MAIN), codec=H264, maxBitrate=2400*1024, minBitrate=1500*1024, width=1280, height=720, maxFps=15
publish(sub):  desc="camera_small"(TRACK_SUB), codec=H264, maxBitrate=160*1024, minBitrate=80*1024, width=320, height=180, maxFps=15

// _480P
capture: deviceId="", position=FRONT, facingMode=USER, width=640, height=480, maxFps=15
publish(main): desc="camera_big"(TRACK_MAIN), codec=H264, maxBitrate=800*1024, minBitrate=400*1024, width=640, height=480, maxFps=15
publish(sub):  desc="camera_small"(TRACK_SUB), codec=H264, maxBitrate=160*1024, minBitrate=80*1024, width=320, height=180, maxFps=15

// _180P
capture: deviceId="", position=FRONT, facingMode=USER, width=320, height=180, maxFps=15
publish(main): desc="camera_big"(TRACK_MAIN), codec=H264, maxBitrate=160*1024, minBitrate=80*1024, width=320, height=180, maxFps=15
publish(sub):  desc="camera_small"(TRACK_SUB), codec=H264, maxBitrate=160*1024, minBitrate=80*1024, width=320, height=180, maxFps=15
```