利用c++ 写一个相机程序 测试相机是否能有码流输出 不依赖opencv

以下是一个简单的 C++ 程序，用于测试相机是否能够输出码流。该程序使用了 V4L2 库，不依赖于 OpenCV 库。你可以根据自己的需要进行修改和调整。

#include <iostream>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>

#define CAMERA_DEVICE "/dev/video0"
#define CAPTURE_WIDTH 640
#define CAPTURE_HEIGHT 480
#define BUFFER_COUNT 1

int main()
{
    // 打开设备
    int camera_fd = open(CAMERA_DEVICE, O_RDWR);
    if (camera_fd == -1) {
        std::cerr << "Failed to open camera device." << std::endl;
        return -1;
    }

    // 查询设备能力
    struct v4l2_capability cap;
    if (ioctl(camera_fd, VIDIOC_QUERYCAP, &cap) == -1) {
        std::cerr << "Failed to query device capabilities." << std::endl;
        close(camera_fd);
        return -1;
    }

    // 设置视频格式
    struct v4l2_format fmt;
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = CAPTURE_WIDTH;
    fmt.fmt.pix.height = CAPTURE_HEIGHT;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_NONE;

    if (ioctl(camera_fd, VIDIOC_S_FMT, &fmt) == -1) {
        std::cerr << "Failed to set video format." << std::endl;
        close(camera_fd);
        return -1;
    }

    // 分配帧缓冲区
    struct v4l2_requestbuffers reqbuf;
    reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    reqbuf.count = BUFFER_COUNT;
    reqbuf.memory = V4L2_MEMORY_MMAP;

    if (ioctl(camera_fd, VIDIOC_REQBUFS, &reqbuf) == -1) {
        std::cerr << "Failed to request buffers." << std::endl;
        close(camera_fd);
        return -1;
    }

    // 映射帧缓冲区
    struct v4l2_buffer buf;
    void *buffer_start[BUFFER_COUNT];
    for (int i = 0; i < BUFFER_COUNT; i++) {
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;

        if (ioctl(camera_fd, VIDIOC_QUERYBUF, &buf) == -1) {
            std::cerr << "Failed to query buffer information." << std::endl;
            close(camera_fd);
            return -1;
        }

        buffer_start[i] = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, camera_fd, buf.m.offset);
        if (buffer_start[i] == MAP_FAILED) {
            std::cerr << "Failed to map buffer." << std::endl;
            close(camera_fd);
            return -1;
        }
    }

    // 将帧缓冲区加入队列
    for (int i = 0; i < BUFFER_COUNT; i++) {
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;

        if (ioctl(camera_fd, VIDIOC_QBUF, &buf) == -1) {
            std::cerr << "Failed to queue buffer." << std::endl;
            close(camera_fd);
            return -1;
        }
    }

    // 开始采集
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (ioctl(camera_fd, VIDIOC_STREAMON, &type) == -1) {
        std::cerr << "Failed to start streaming." << std::endl;
        close(camera_fd);
        return -1;
    }

    // 从队列中取出帧缓冲区
    while (true) {
        fd_set fds;
        FD_ZERO(&fds);
        FD_SET(camera_fd, &fds);

        timeval tv;
        tv.tv_sec = 2;
        tv.tv_usec = 0;

        int r = select(camera_fd + 1, &fds, NULL, NULL, &tv);
        if (r == -1) {
            std::cerr << "Failed to select." << std::endl;
            close(camera_fd);
            return -1;
        } else if (r == 0) {
            std::cerr << "Select timeout." << std::endl;
            close(camera_fd);
            return -1;
        }

        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;

        if (ioctl(camera_fd, VIDIOC_DQBUF, &buf) == -1) {
            std::cerr << "Failed to dequeue buffer." << std::endl;
            close(camera_fd);
            return -1;
        }

        // 在这里处理图像数据，例如保存到文件或者显示到屏幕上

        if (ioctl(camera_fd, VIDIOC_QBUF, &buf) == -1) {
            std::cerr << "Failed to queue buffer." << std::endl;
            close(camera_fd);
            return -1;
        }
    }

    // 停止采集
    if (ioctl(camera_fd, VIDIOC_STREAMOFF, &type) == -1) {
        std::cerr << "Failed to stop streaming." << std::endl;
        close(camera_fd);
        return -1;
    }

    // 释放帧缓冲区
    for (int i = 0; i < BUFFER_COUNT; i++) {
        if (munmap(buffer_start[i], buf.length) == -1) {
            std::cerr << "Failed to unmap buffer." << std::endl;
            close(camera_fd);
            return -1;
        }
    }

    // 关闭设备
    close(camera_fd);

    return 0;
}

该程序首先打开设备 `/dev/video0`，然后查询设备能力和设置视频格式。接着分配和映射帧缓冲区，并将其加入队列。程序进入循环后，从队列中取出帧缓冲区并处理图像数据，然后将其重新加入队列。最后停止采集，释放帧缓冲区，并关闭设备。

你可以在程序中添加代码来处理图像数据，例如将其保存到文件或者显示到屏幕上。在这个例子中，我们只是简单地取出了帧缓冲区，没有进行任何处理。如果相机能够输出码流，那么程序应该能够正常运行并输出一些调试信息。