> ## 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.

# Custom video preset

> Android custom video preset PreOptionCustomVideo for LocalCustomVideoTrack: capture options that describe the external frame source, publish options, and the built-in def (TRACK_CUSTOM) and screen (TRACK_SHARE) presets. Read when publishing external YUV frames on Android.

This page describes the custom video preset `PreOptionCustomVideo`, used by the [`LocalCustomVideoTrack`](/en/rtc/android/api-reference/LocalCustomVideoTrack) obtained from [`RTCEngine.getLocalCustomVideoTrack`](/en/rtc/android/api-reference/RTCEngine) (which pushes external raw YUV frames into a published track). For the general preset structure (capture options + publish options) and `PublishCustomOptions` used at publish time, see [Camera preset](/en/rtc/android/presets/camera).

## PreOptionCustomVideo

Purpose: The custom video track preset, combining custom capture parameters with video publish parameters.

### Structure

`PreOptionCustomVideo(capture: CustomVideoCaptureOptions, publish: VideoPublishOptions)`

| Property | Data type | Description |
| - | - | - |
| capture | `CustomVideoCaptureOptions` | Custom video capture-side parameters. |
| publish | `VideoPublishOptions` | Custom video publish parameters. |

### Capture options CustomVideoCaptureOptions

Purpose: Declares the specifications of the external frame source, which the SDK uses as a reference when creating the published track. The SDK doesn't capture custom video itself; your app feeds the actual frames through `LocalCustomVideoTrack.inputData`.

| Property | Data type | Description |
| - | - | - |
| width | `Int` | Capture width. |
| height | `Int` | Capture height. |
| maxFps | `Int` | Capture frame rate. |
| maxBitrate | `Int` | Capture bitrate. |

### Publish options VideoPublishOptions

Purpose: Same structure as the video publish parameters (for fields, see [Camera preset](/en/rtc/android/presets/camera)).

* The default custom video preset uses `desc = TRACK_CUSTOM` (`"custom"`)
* The screen scenario preset uses `desc = TRACK_SHARE` (`"screen"`)
* Custom video doesn't use simulcast; `simulcasts` is always `null`

### Built-in presets

Purpose: The SDK provides two custom video presets, `PreOptionCustomVideo.def` and `PreOptionCustomVideo.screen`.

```kotlin theme={null}
// def — default custom stream, track description custom
capture: width=1920, height=1080, maxFps=10, maxBitrate=1024*1024
publish: desc="custom"(TRACK_CUSTOM), codec=H264, maxBitrate=1024*1024,
         width=1920, height=1080, maxFps=10, props=null, simulcasts=null

// screen — publishes external video with the screen sharing track description
capture: width=1920, height=1080, maxFps=10, maxBitrate=1024*1024
publish: desc="screen"(TRACK_SHARE), codec=H264, maxBitrate=1024*1024,
         width=1920, height=1080, maxFps=10, props=null, simulcasts=null
```

### Recommendations

* Keep the frame resolution you push consistent with `publish.width` / `publish.height` to avoid extra scaling overhead; don't exceed `maxFps`.
* To appear as "sharing" to remote users, use `PreOptionCustomVideo.screen`, or override `desc` with `PublishCustomOptions(desc = TrackDesc.TRACK_SHARE.value)` in `publishLocalVideo`.
* The SDK caches the track instance as a singleton; getting it again overwrites the old `preOpt` with the new one, so republish after switching presets.
* For the full publishing flow, see [Custom tracks](/en/rtc/android/advanced/custom-track).