v4l2打开摄像头代码 c++

以下是一个简单的v4l2打开摄像头的C代码示例：

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

#define CAMERA_DEVICE "/dev/video0"

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

int main(int argc, char **argv)
{
    int fd = -1;
    struct buffer *buffers = NULL;
    unsigned int n_buffers = 0;

    // 1. 打开摄像头设备
    fd = open(CAMERA_DEVICE, O_RDWR | O_NONBLOCK, 0);
    if (fd == -1) {
        fprintf(stderr, "Error opening device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
        return EXIT_FAILURE;
    }

    // 2. 查询摄像头设备信息
    struct v4l2_capability cap;
    if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1) {
        fprintf(stderr, "Error querying device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
        goto fail;
    }

    // 3. 设置摄像头采集格式
    struct v4l2_format fmt;
    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = 640;
    fmt.fmt.pix.height = 480;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
    if (ioctl(fd, VIDIOC_S_FMT, &fmt) == -1) {
        fprintf(stderr, "Error setting format on device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
        goto fail;
    }

    // 4. 请求摄像头缓冲区
    struct v4l2_requestbuffers req;
    memset(&req, 0, sizeof(req));
    req.count = 4;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;
    if (ioctl(fd, VIDIOC_REQBUFS, &req) == -1) {
        fprintf(stderr, "Error requesting buffers on device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
        goto fail;
    }

    // 5. 映射摄像头缓冲区到用户空间
    buffers = calloc(req.count, sizeof(*buffers));
    if (buffers == NULL) {
        fprintf(stderr, "Error allocating memory for buffers: %d, %s\n", errno, strerror(errno));
        goto fail;
    }
    for (n_buffers = 0; n_buffers < req.count; n_buffers++) {
        struct v4l2_buffer buf;
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = n_buffers;
        if (ioctl(fd, VIDIOC_QUERYBUF, &buf) == -1) {
            fprintf(stderr, "Error querying buffer %d on device %s: %d, %s\n", n_buffers, CAMERA_DEVICE, errno, strerror(errno));
            goto fail;
        }
        buffers[n_buffers].length = buf.length;
        buffers[n_buffers].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
        if (buffers[n_buffers].start == MAP_FAILED) {
            fprintf(stderr, "Error mapping buffer %d on device %s: %d, %s\n", n_buffers, CAMERA_DEVICE, errno, strerror(errno));
            goto fail;
        }
    }

    // 6. 启动摄像头采集
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (ioctl(fd, VIDIOC_STREAMON, &type) == -1) {
        fprintf(stderr, "Error starting capture on device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
        goto fail;
    }

    // 7. 采集图像并处理
    printf("Press Ctrl-C to stop.\n");
    while (1) {
        fd_set fds;
        FD_ZERO(&fds);
        FD_SET(fd, &fds);
        struct timeval tv = {0};
        tv.tv_sec = 2;
        int r = select(fd + 1, &fds, NULL, NULL, &tv);
        if (r == -1) {
            if (errno == EINTR) continue;
            fprintf(stderr, "Error waiting for frame on device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
            goto fail;
        }
        if (r == 0) {
            fprintf(stderr, "Error waiting for frame on device %s: select timeout\n", CAMERA_DEVICE);
            goto fail;
        }

        struct v4l2_buffer buf;
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        if (ioctl(fd, VIDIOC_DQBUF, &buf) == -1) {
            fprintf(stderr, "Error dequeueing buffer on device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
            goto fail;
        }

        // 在这里处理采集到的图像数据
        printf("Got a frame with %d bytes\n", buf.bytesused);

        if (ioctl(fd, VIDIOC_QBUF, &buf) == -1) {
            fprintf(stderr, "Error queueing buffer on device %s: %d, %s\n", CAMERA_DEVICE, errno, strerror(errno));
            goto fail;
        }
    }

    return EXIT_SUCCESS;

fail:
    if (buffers != NULL) {
        for (unsigned int i = 0; i < n_buffers; i++) {
            if (buffers[i].start != MAP_FAILED) munmap(buffers[i].start, buffers[i].length);
        }
        free(buffers);
    }
    if (fd != -1) close(fd);
    return EXIT_FAILURE;
}