> ## 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.

# Screen sharing

> Share the screen with the Web SDK: create, capture, preview, and publish a LocalScreenTrack, handle the browser's built-in Stop sharing button via TRACK_ENDED, capture system audio, ScreenCaptureOptions parameters, and the ScreenPresets.

### Basic screen sharing

Screen sharing uses `LocalScreenTrack`, and the flow is similar to the camera:

```typescript theme={null}
import {
  SRTC,
  LocalScreenTrack,
  ScreenPresets,
  ChannelEventType,
} from '@seastart/srtc-web-sdk';

const srtc = new SRTC();
let localScreenTrack: LocalScreenTrack | undefined;

const openScreen = async () => {
  // Create a screen sharing track with the 1080p preset
  localScreenTrack = srtc.createLocalScreenTrack(ScreenPresets['1080p']);

  // Start capture (the browser shows a screen picker)
  await localScreenTrack.startCapture();

  // Local preview (optional)
  localScreenTrack.addPlayView(document.querySelector<HTMLElement>('#screen-preview')!);

  // Publish
  await srtc.publishLocalTrack(localScreenTrack, { desc: 'screen' });
};

const closeScreen = async () => {
  if (!localScreenTrack) return;
  await srtc.unpublishLocalTrack(localScreenTrack);
  localScreenTrack.removeAllPlayViews();
  localScreenTrack.stopCapture();
  localScreenTrack = undefined;
};
```

***

### Handle the browser's built-in "Stop sharing" button

When the user clicks the "Stop sharing" button at the bottom of the browser, the SDK fires the `TRACK_ENDED` event, and you need to clean up state in the event callback:

```typescript theme={null}
srtc.onNotifyChannelEvent = async (evt) => {
  if (evt.type === ChannelEventType.TRACK_ENDED) {
    if (evt.data === localScreenTrack) {
      // The user clicked the browser's "Stop sharing"; clean up proactively
      await closeScreen();
      // Update your UI state (e.g., hide the "Sharing" indicator)
    }
  }
};
```

***

### Capture system audio at the same time

Some browsers (Chrome 74+, Windows/macOS) support capturing **system audio** (such as audio from a playing video) while sharing the screen.

`createLocalScreenTrack` accepts a second parameter `audioPreset`; when you pass it, the SDK also captures system audio if the system supports it:

```typescript theme={null}
import {
  SRTC,
  LocalScreenTrack,
  ScreenPresets,
  ScreenAudioPresets,
} from '@seastart/srtc-web-sdk';

const srtc = new SRTC();

// Create a screen sharing track and request system audio capture at the same time
const localScreenTrack = srtc.createLocalScreenTrack(
  ScreenPresets['1080p'],
  ScreenAudioPresets.default,  // Second parameter: system audio preset
);

await localScreenTrack.startCapture();

// Get the system audio track (if the browser supports it and the user checked "Share audio")
const screenAudioTrack = localScreenTrack.getAudioTrack();
if (screenAudioTrack) {
  // Publish the system audio to the channel too
  await srtc.publishLocalTrack(screenAudioTrack, { desc: 'screen_audio' });
  console.log('System audio published');
} else {
  console.warn('System audio capture is not supported in this environment, or the user did not check "Share audio"');
}

// Publish the screen sharing video
await srtc.publishLocalTrack(localScreenTrack, { desc: 'screen' });
```

> **Note:**
>
> * System audio capture is only reliably supported in Chrome (Windows/macOS)
> * Safari and Firefox don't support system audio capture
> * The user must check "Share audio" in the browser dialog for `getAudioTrack()` to return a valid track
> * When you stop sharing, remember to also call `unpublishLocalTrack(screenAudioTrack)` and `stopCapture()`

***

### ScreenCaptureOptions parameters

You can pass the following parameters when calling `localScreenTrack.startCapture(options)`:

| Parameter | Type | Description |
| - | - | - |
| `width` | `number` | Desired capture width |
| `height` | `number` | Desired capture height |
| `frameRate` | `number` | Desired frame rate |
| `contentHint` | `'motion' \| 'detail' \| 'text'` | Content type hint that affects the encoding strategy: `motion` suits video/games, `detail` suits images/graphics, `text` suits documents/code |
| `showCursor` | `boolean` | Whether to show the mouse cursor |
| `rect` | `{ x, y, w, h }` | Region cropping parameter on Windows; on other platforms just pass `{ x: 0, y: 0, w: 0, h: 0 }` |

```typescript theme={null}
await localScreenTrack.startCapture({
  frameRate: 15,
  contentHint: 'detail',  // Use when sharing documents/code to improve sharpness
  showCursor: true,
});
```

***

### Presets (ScreenPresets)

| Preset | Resolution | Frame rate | Bitrate | Description |
| - | :-: | :-: | :-: | - |
| `ScreenPresets['1080p']` | 1920×1080 | 10 fps | 2 Mbps | Default preset; medium priority and maintain-resolution degradation by default |
| `ScreenPresets['720p']` | 1280×720 | 10 fps | 1.5 Mbps | Medium priority and maintain-resolution degradation by default |