写一个linuxC语言使用v4l2调用摄像头的代码

以下是一个简单的使用v4l2调用摄像头的Linux C语言代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <fcntl.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <sys/mman.h>
#include <linux/videodev2.h>

#define CAMERA_DEVICE "/dev/video0"
#define CAPTURE_FILE "capture.yuv"
#define IMAGE_WIDTH 640
#define IMAGE_HEIGHT 480
#define BUFFER_COUNT 4

struct buffer {
    void *start;
    size_t length;
};

static struct buffer buffers[BUFFER_COUNT];
static int camera_fd = -1;

static int init_camera()
{
    struct v4l2_capability cap;
    struct v4l2_format fmt;
    struct v4l2_requestbuffers req;
    struct v4l2_buffer buf;
    unsigned int i;

    camera_fd = open(CAMERA_DEVICE, O_RDWR);
    if (camera_fd == -1) {
        perror("Failed to open camera device");
        return -1;
    }

    if (ioctl(camera_fd, VIDIOC_QUERYCAP, &cap) == -1) {
        perror("Failed to query camera capabilities");
        return -1;
    }

    if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
        fprintf(stderr, "Camera device does not support video capture\n");
        return -1;
    }

    if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
        fprintf(stderr, "Camera device does not support streaming I/O\n");
        return -1;
    }

    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = IMAGE_WIDTH;
    fmt.fmt.pix.height = IMAGE_HEIGHT;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;

    if (ioctl(camera_fd, VIDIOC_S_FMT, &fmt) == -1) {
        perror("Failed to set camera format");
        return -1;
    }

    memset(&req, 0, sizeof(req));
    req.count = BUFFER_COUNT;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;

    if (ioctl(camera_fd, VIDIOC_REQBUFS, &req) == -1) {
        perror("Failed to request camera buffers");
        return -1;
    }

    for (i = 0; i < req.count; i++) {
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;

        if (ioctl(camera_fd, VIDIOC_QUERYBUF, &buf) == -1) {
            perror("Failed to query camera buffer");
            return -1;
        }

        buffers[i].length = buf.length;
        buffers[i].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, camera_fd, buf.m.offset);
        if (buffers[i].start == MAP_FAILED) {
            perror("Failed to map camera buffer");
            return -1;
        }
    }

    for (i = 0; i < req.count; i++) {
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;

        if (ioctl(camera_fd, VIDIOC_QBUF, &buf) == -1) {
            perror("Failed to enqueue camera buffer");
            return -1;
        }
    }

    return 0;
}

static int start_capture()
{
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (ioctl(camera_fd, VIDIOC_STREAMON, &type) == -1) {
        perror("Failed to start camera capture");
        return -1;
    }

    return 0;
}

static int stop_capture()
{
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (ioctl(camera_fd, VIDIOC_STREAMOFF, &type) == -1) {
        perror("Failed to stop camera capture");
        return -1;
    }

    return 0;
}

static int capture_image()
{
    fd_set fds;
    struct timeval tv;
    struct v4l2_buffer buf;
    unsigned int i;
    int ret;

    FD_ZERO(&fds);
    FD_SET(camera_fd, &fds);

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

    ret = select(camera_fd + 1, &fds, NULL, NULL, &tv);
    if (ret == -1) {
        perror("Failed to wait for camera capture");
        return -1;
    }

    if (ret == 0) {
        fprintf(stderr, "Camera capture timeout\n");
        return -1;
    }

    memset(&buf, 0, sizeof(buf));
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;

    if (ioctl(camera_fd, VIDIOC_DQBUF, &buf) == -1) {
        perror("Failed to dequeue camera buffer");
        return -1;
    }

    FILE *fp = fopen(CAPTURE_FILE, "wb");
    if (fp == NULL) {
        perror("Failed to open capture file");
        return -1;
    }

    fwrite(buffers[buf.index].start, buf.bytesused, 1, fp);
    fclose(fp);

    if (ioctl(camera_fd, VIDIOC_QBUF, &buf) == -1) {
        perror("Failed to enqueue camera buffer");
        return -1;
    }

    return 0;
}

static void cleanup_camera()
{
    unsigned int i;

    for (i = 0; i < BUFFER_COUNT; i++) {
        if (munmap(buffers[i].start, buffers[i].length) == -1) {
            perror("Failed to unmap camera buffer");
        }
    }

    if (camera_fd != -1) {
        close(camera_fd);
    }
}

int main()
{
    if (init_camera() == -1) {
        return EXIT_FAILURE;
    }

    if (start_capture() == -1) {
        cleanup_camera();
        return EXIT_FAILURE;
    }

    if (capture_image() == -1) {
        stop_capture();
        cleanup_camera();
        return EXIT_FAILURE;
    }

    if (stop_capture() == -1) {
        cleanup_camera();
        return EXIT_FAILURE;
    }

    cleanup_camera();
    return EXIT_SUCCESS;
}

这个程序使用v4l2接口从摄像头捕获一张图像，并将其保存为YUV格式的文件。你可以根据需要修改图像的宽度、高度和像素格式。