基于V4L2的简单视频采集

编译环境：ubuntu12.04

编译器：arm-linux-gcc 4.4.1

目标板：迅为iTOP4412 （cortex A9）

 

程序实现功能：捕获一帧图像。

代码：

#include 
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#include 
#include 

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

struct buffer *buffers;
unsigned long n_buffers;
unsigned long file_length;

int file_fd;
char *dev_name = "/dev/video4";
int fd;


/*获取一帧图像*/
static int read_frame(void)
{
    struct v4l2_buffer buf;

    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    ioctl(fd, VIDIOC_DQBUF, &buf);  //出队，从队列中取出一个缓冲帧

    write(file_fd, buffers[buf.index].start, buffers[buf.index].length);  //将图片写入图像件“test.jpg”

    ioctl(fd, VIDIOC_QBUF, &buf); //重新入队

    return 1;

}

int main(int argc, char **argv)
{
    struct v4l2_capability cap;
    struct v4l2_format fmt;
    struct v4l2_requestbuffers req;
    struct v4l2_buffer buf;

    file_fd = open("test.jpg", O_RDWR | O_CREAT, 0777);
    fd = open(dev_name, O_RDWR | O_NONBLOCK, 0);  //非阻塞方式打开摄像头
    if (fd < 0)
    {
        perror("open device failed!");
        return -1;
    }

    /*获取摄像头信息*/
    if (ioctl(fd, VIDIOC_QUERYCAP, &cap) < 0)
    {
        perror("get info failed!");
        return -1;
    }
    printf("Driver Name:%s\n Card Name:%s\n Bus info:%s\n\n ", cap.driver, cap.card, cap.bus_info);

    /*************************************************************************************
    //查询所有支持的格式
    struct v4l2_fmtdesc fmtdesc;
    fmtdesc.index = 0;
    fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc) != -1)
    {
        printf("VIDIOC_ENUM_FMT success! fmtdesc.description: %s\n",fmtdesc.description);
        fmtdesc.index++;
    }
    *************************************************************************************/

    /*设置摄像头捕捉帧格式及分辨率*/
    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    fmt.fmt.pix.width = 640;   //帧宽
    fmt.fmt.pix.height = 480;  //帧高
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG; //数据存储类型设为MJPEG，采集到的即为一张完整的jpg图像

    if (ioctl(fd, VIDIOC_S_FMT, &fmt) < 0)
    {
        perror("set fmt failed!");
        return -1;
    }

    /*申请4个图像缓冲区（位于内核空间）*/
    req.count = 4;    //缓存数量，即缓存队列里保持多少张照片，一般不超过5个
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP; //MMAP内存映射方式
    ioctl(fd, VIDIOC_REQBUFS, &req);

    buffers = calloc(req.count, sizeof(*buffers));

    /*将申请的4个缓冲区映射到用户空间*/
    for (n_buffers = 0; n_buffers < req.count; ++n_buffers)
    {
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = n_buffers;

        ioctl(fd, VIDIOC_QUERYBUF, &buf);

        buffers[n_buffers].length = buf.length;

        buffers[n_buffers].start = mmap(NULL,
                                        buf.length,
                                        PROT_READ | PROT_WRITE,
                                        MAP_SHARED,
                                        fd,
                                        buf.m.offset);
    }

    /*缓冲区入队列*/
    int i;
    for (i = 0; i < n_buffers; ++i)
    {
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = i;
        ioctl(fd, VIDIOC_QBUF, &buf);
    }

    /*使能视频设备输出视频流*/
    enum v4l2_buf_type type;
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    ioctl(fd, VIDIOC_STREAMON, &type);

    /*select监听*/
    fd_set fds;

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

    select(fd + 1, &fds, NULL, NULL, NULL);

    read_frame();
    
    for (i = 0; i < n_buffers; ++i)
        munmap(buffers[i].start, buffers[i].length);

    close(fd);
    close(file_fd);
    printf("Camera Capture Done.\n");

    return 0;


}