> ## 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.

# Integration

> What the SRTC C SDK does and doesn't do, supported platforms and architectures, the library files in the package, and how to compile and link them. Read this page before integrating the C SDK into a server-side or embedded project.

The SRTC C SDK is an audio and video SDK for **server-side and embedded** scenarios. It exposes a pure C interface (`rtc_*` functions and `rtc_*_t` structs, declared with `extern "C"`), so both C and C++ projects can use it directly.

### Use cases

* Server-side recording, transcoding, and re-streaming
* The publishing side of an MCU composite stream
* Connecting AI agents / voice bots to a channel
* Publishing and receiving on embedded devices (Linux ARM boards)

### What the SDK does and doesn't do

This SDK **doesn't include** client-side capabilities such as camera capture, microphone capture, video rendering, device management, or beauty filters:

* **Publishing**: you handle capture and encoding, and hand the encoded H.264 / H.265 / Opus / AAC raw data to the SDK through `rtc_write_sample`
* **Receiving**: the SDK hands you the remote encoded data through callbacks; decoding and rendering are up to you

If you're building a desktop client, use the [Windows SDK](/zh/rtc/windows/integration) (Chinese) instead. It has a C++ interface and includes capture and rendering.

***

### SDK package contents

| File | Description |
| - | - |
| `librtc.h` | C interface header |
| `librtc.so` | Dynamic library (Linux) |
| `librtc.a` | Static library (Linux / Windows, GNU ar format, for the GCC and MinGW toolchains) |
| `librtc.dll` | Dynamic library (Windows) |
| `librtc.lib` | Import library (Windows), used by MSVC to link against `librtc.dll` |
| `librtc.dylib` | Dynamic library (macOS) |

<Note>
  For MSVC (Visual Studio) projects, use `librtc.dll` + `librtc.lib`. You can't link `librtc.a` directly.
</Note>

***

### Supported platforms

| Platform | Architecture | Library files provided |
| - | - | - |
| Linux (glibc) | x86\_64 | `librtc.so`, `librtc.a` |
| Linux (glibc) | aarch64 | `librtc.so`, `librtc.a` |
| Linux (musl / Alpine) | aarch64 | `librtc.so` |
| Linux | armv7 (32-bit) | `librtc.so`, `librtc.a` |
| Windows | x86\_64 | `librtc.dll`, `librtc.lib`, `librtc.a` |
| macOS | Apple Silicon (arm64) | `librtc.dylib` (for local development and debugging) |

<Warning>
  **Choose the library that matches the target system's libc.** Mainstream distributions (CentOS / Ubuntu / Debian, etc.) use the glibc build, and Alpine uses the musl build. The two can't be mixed.

  The Alpine (musl) platform only provides the dynamic library `librtc.so`, not a static library.
</Warning>

If you need a platform or architecture not listed above, contact us.

<Warning>
  **When upgrading the SDK, recompile with the new `librtc.h`**—don't just replace the library files. When struct fields are added or removed (for example, 0.0.9 removed `rtc_user_info_t.link_id`), a program built with the old header reads the wrong fields. For changes in each version, see the [Changelog](/en/rtc/capi/changelog).
</Warning>

***

### Compiling and linking

Include the header:

```c theme={null}
#include "librtc.h"
```

Link the dynamic library with GCC / Clang:

```bash theme={null}
gcc -Wall -I/path/to/sdk -o myapp main.c \
    -L/path/to/sdk -lrtc -lpthread -lm
```

At runtime the system needs to be able to find `librtc.so`:

```bash theme={null}
export LD_LIBRARY_PATH=/path/to/sdk:$LD_LIBRARY_PATH
```

You can also hard-code the search path at link time so you don't have to set the environment variable every time:

```bash theme={null}
gcc -o myapp main.c -L/path/to/sdk -lrtc -lpthread -lm -Wl,-rpath,/path/to/sdk
```

<Tip>
  If you get `error while loading shared libraries: librtc.so` at runtime, the library search path isn't set correctly: check `LD_LIBRARY_PATH` or `-rpath`, or copy `librtc.so` into a system library directory.
</Tip>

***

### Media streaming engine

Which media streaming engine a channel uses is determined by the channel configuration sent down by the server. Your code doesn't need to care about it or configure anything.

Some capabilities (simulcast layer switching, network quality reporting, active speaker) are only available with the SeaStart engine; with other engines the corresponding callbacks never fire—see [SeaStart advanced features](/en/rtc/capi/advanced/seastart). Make sure your application still works without these callbacks.

***

### Next steps

* [Quickstart](/en/rtc/capi/quickstart): get receiving and publishing working in 10 minutes
* [API reference](/en/rtc/capi/api-reference/engine): the complete API reference