Function set_fps

rustcv-camera/src/backend/linux/sys.rs:215–227

Set the frame rate via VIDIOC_S_PARM. 通过 VIDIOC_S_PARM 设置帧率。 Frame rate is expressed as a fraction: `timeperframe = numerator / denominator`. For 30fps: numerator=1, denominator=30. 帧率用分数表示：`timeperframe = 分子 / 分母`。 30fps 对应：分子=1，分母=30。

(fd: RawFd, fps: u32)

/// 帧率用分数表示：`timeperframe = 分子 / 分母`。
/// 30fps 对应：分子=1，分母=30。
pub fn set_fps(fd: RawFd, fps: u32) -> io::Result<v4l2_streamparm> {
    let mut parm: v4l2_streamparm = unsafe { std::mem::zeroed() };
    parm.type_ = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    let capture = unsafe { &mut parm.parm.capture };
    capture.timeperframe.numerator = 1;
    capture.timeperframe.denominator = fps;

    unsafe {
        v4l2_ioctl(fd, VIDIOC_S_PARM, &mut parm as *mut _ as *mut libc::c_void)?;
    }
    Ok(parm)
}

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