video4linux2 example, v4l2 Options

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 v4l2_test.tar.gz ( 2.14k ) Number of downloads: 248

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v4l2-test1.c

代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>

#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#include <asm/types.h>
#include <linux/videodev2.h>

#define CLEAR(x) memset (&(x), 0, sizeof (x))

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

static char    *dev_name = "/dev/video0";
static int      fd = -1;
struct buffer  *buffers = NULL;

FILE           *file_fd;
static unsigned long file_length;
static unsigned char *file_name;

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

    file_fd = fopen("test.jpg", "w");

    fd = open(dev_name, O_RDWR /* required */  | O_NONBLOCK, 0);

    ioctl(fd, VIDIOC_QUERYCAP, &cap);

    CLEAR(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;
    ioctl(fd, VIDIOC_S_FMT, &fmt);

    file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;

    buffers = calloc(1, sizeof(*buffers));

    buffers[0].length = file_length;
    buffers[0].start = malloc(file_length);

    for (;;) {
        fd_set          fds;
        struct timeval  tv;
        int             r;

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

        /*
         * Timeout.
         */
        tv.tv_sec = 3;
        tv.tv_usec = 0;

        r = select(fd + 1, &fds, NULL, NULL, &tv);

        if (-1 == r) {
            if (EINTR == errno)
                continue;
            printf("select");
        }

        if (0 == r) {
            fprintf(stderr, "select timeout\n");
            exit(EXIT_FAILURE);
        }

        if (read(fd, buffers[0].start, buffers[0].length))
            break;
    }

    fwrite(buffers[0].start, buffers[0].length, 1, file_fd);

    free(buffers[0].start);
    close(fd);
    fclose(file_fd);
    exit(EXIT_SUCCESS);
    return 0;
}

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v4l2-test2.c

代码

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>

#include <getopt.h>

#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <malloc.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/time.h>
#include <sys/mman.h>
#include <sys/ioctl.h>

#include <asm/types.h>
#include <linux/videodev2.h>

#define CLEAR(x) memset (&(x), 0, sizeof (x))

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

static char    *dev_name = "/dev/video0";    // 摄像头设备名
static int      fd = -1;
struct buffer  *buffers = NULL;
static unsigned int n_buffers = 0;

FILE           *file_fd;
static unsigned long file_length;
static unsigned char *file_name;
// ////////////////////////////////////////////////////
// 获取一帧数据
// ////////////////////////////////////////////////////
static int
read_frame(void)
{
    struct v4l2_buffer buf;
    unsigned int    i;

    CLEAR(buf);
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;

    ioctl(fd, VIDIOC_DQBUF, &buf);    // 出列采集的帧缓冲

    assert(buf.index < n_buffers);
    printf("buf.index dq is %d,\n", buf.index);

    fwrite(buffers[buf.index].start, buffers[buf.index].length, 1, file_fd);    // 将其写入文件中

    ioctl(fd, VIDIOC_QBUF, &buf);    // 再将其入列

    return 1;
}

int
main(int argc, char **argv)
{
    struct v4l2_capability cap;
    struct v4l2_format fmt;
    unsigned int    i;
    enum v4l2_buf_type type;

    file_fd = fopen("test-mmap.jpg", "w");    // 图片文件名

    fd = open(dev_name, O_RDWR /* required */  | O_NONBLOCK, 0);    // 打开设备

    ioctl(fd, VIDIOC_QUERYCAP, &cap);    // 获取摄像头参数

    CLEAR(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;
    ioctl(fd, VIDIOC_S_FMT, &fmt);    // 设置图像格式

    file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;    // 计算图片大小

    struct v4l2_requestbuffers req;
    CLEAR(req);
    req.count = 4;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;

    ioctl(fd, VIDIOC_REQBUFS, &req);    // 申请缓冲，count是申请的数量

    if (req.count < 2)
        printf("Insufficient buffer memory\n");

    buffers = calloc(req.count, sizeof(*buffers));    // 内存中建立对应空间

    for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
        struct v4l2_buffer buf;    // 驱动中的一帧
        CLEAR(buf);
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        buf.index = n_buffers;

        if (-1 == ioctl(fd, VIDIOC_QUERYBUF, &buf))    // 映射用户空间
            printf("VIDIOC_QUERYBUF error\n");

        buffers[n_buffers].length = buf.length;
        buffers[n_buffers].start = mmap(NULL /* start anywhere */ ,    // 通过mmap建立映射关系
                        buf.length, PROT_READ | PROT_WRITE    /* required
                                             */ ,
                        MAP_SHARED    /* recommended
                                 */ ,
                        fd, buf.m.offset);

        if (MAP_FAILED == buffers[n_buffers].start)
            printf("mmap failed\n");
    }

    for (i = 0; i < n_buffers; ++i) {
        struct v4l2_buffer buf;
        CLEAR(buf);

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

        if (-1 == ioctl(fd, VIDIOC_QBUF, &buf))    // 申请到的缓冲进入列队
            printf("VIDIOC_QBUF failed\n");
    }

    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (-1 == ioctl(fd, VIDIOC_STREAMON, &type))    // 开始捕捉图像数据
        printf("VIDIOC_STREAMON failed\n");

    for (;;)        // 这一段涉及到异步IO
    {
        fd_set          fds;
        struct timeval  tv;
        int             r;

        FD_ZERO(&fds);    // 将指定的文件描述符集清空
        FD_SET(fd, &fds);    // 在文件描述符集合中增加一个新的文件描述符

        /*
         * Timeout.
         */
        tv.tv_sec = 2;
        tv.tv_usec = 0;

        r = select(fd + 1, &fds, NULL, NULL, &tv);    // 判断是否可读（即摄像头是否准备好），tv是定时

        if (-1 == r) {
            if (EINTR == errno)
                continue;
            printf("select err\n");
        }
        if (0 == r) {
            fprintf(stderr, "select timeout\n");
            exit(EXIT_FAILURE);
        }

        if (read_frame())    // 如果可读，执行read_frame
                    // ()函数，并跳出循环
            break;
    }

      unmap:
    for (i = 0; i < n_buffers; ++i)
        if (-1 == munmap(buffers[i].start, buffers[i].length))
            printf("munmap error");
    close(fd);
    fclose(file_fd);
    exit(EXIT_SUCCESS);
    return 0;
}