V4L 操作的demo

以下是一个简单的使用V4L进行视频采集的demo代码，仅供参考：

#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 WIDTH 640
#define HEIGHT 480
#define BUFFER_COUNT 2

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

int main(void)
{
    int fd = open("/dev/video0", O_RDWR);
    if (fd < 0) {
        perror("open");
        exit(1);
    }

    // 查询设备的功能和属性
    struct v4l2_capability cap;
    if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0) {
        perror("VIDIOC_QUERYCAP");
        exit(1);
    }

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

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

    // 设置视频格式
    struct v4l2_format fmt;
    memset(&fmt, 0, sizeof(fmt));
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = WIDTH;
    fmt.fmt.pix.height = HEIGHT;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
    if (ioctl(fd, VIDIOC_S_FMT, &fmt) < 0) {
        perror("VIDIOC_S_FMT");
        exit(1);
    }

    // 请求内存缓冲区
    struct v4l2_requestbuffers reqbuf;
    memset(&reqbuf, 0, sizeof(reqbuf));
    reqbuf.count = BUFFER_COUNT;
    reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    reqbuf.memory = V4L2_MEMORY_MMAP;
    if (ioctl(fd, VIDIOC_REQBUFS, &reqbuf) < 0) {
        perror("VIDIOC_REQBUFS");
        exit(1);
    }

    // 映射内存缓冲区
    struct buffer buffers[BUFFER_COUNT];
    for (int i = 0; i < BUFFER_COUNT; i++) {
        struct v4l2_buffer buf;
        memset(&buf, 0, sizeof(buf));
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        if (ioctl(fd, VIDIOC_QUERYBUF, &buf) < 0) {
            perror("VIDIOC_QUERYBUF");
            exit(1);
        }

        buffers[i].length = buf.length;
        buffers[i].start = mmap(NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
        if (buffers[i].start == MAP_FAILED) {
            perror("mmap");
            exit(1);
        }

        if (ioctl(fd, VIDIOC_QBUF, &buf) < 0) {
            perror("VIDIOC_QBUF");
            exit(1);
        }
    }

    // 启动视频流
    enum v4l2_buf_type type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if (ioctl(fd, VIDIOC_STREAMON, &type) < 0) {
        perror("VIDIOC_STREAMON");
        exit(1);
    }

    // 从队列中取出缓冲区并处理
    for (int i = 0; i < BUFFER_COUNT; i++) {
        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) < 0) {
            perror("VIDIOC_DQBUF");
            exit(1);
        }

        // 处理图像数据
        // ...

        if (ioctl(fd, VIDIOC_QBUF, &buf) < 0) {
            perror("VIDIOC_QBUF");
            exit(1);
        }
    }

    // 停止视频流
    if (ioctl(fd, VIDIOC_STREAMOFF, &type) < 0) {
        perror("VIDIOC_STREAMOFF");
        exit(1);
    }

    // 释放内存缓冲区
    for (int i = 0; i < BUFFER_COUNT; i++) {
        munmap(buffers[i].start, buffers[i].length);
    }

    close(fd);
    return 0;
}

以上代码仅供参考，具体实现可能因设备和操作系统而异。