video capture.c

Video for linux head two 的视频采集示例

/*
 *  V4L2 video capture example
 *
 *  This program can be used and distributed without restrictions.
 */

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

#include <getopt.h>             /* getopt_long() */

#include <fcntl.h>              /* low-level i/o */
#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>          /* for videodev2.h */

#include <linux/videodev2.h>

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

typedef enum {
        IO_METHOD_READ,
        IO_METHOD_MMAP,
        IO_METHOD_USERPTR,
} io_method;

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

static char *           dev_name        = NULL;
static io_method        io              = IO_METHOD_MMAP;
static int              fd              = -1;
struct buffer *         buffers         = NULL;
static unsigned int     n_buffers       = 0;

static void errno_exit(const char *s)
{
        fprintf(stderr, "%s error %d, %s\n",
                 s, errno, strerror(errno));

        exit(EXIT_FAILURE);
}

static int xioctl(int fd,int request,void *arg)
{
        int r;

        do r = ioctl(fd, request, arg);
        while (-1 == r && EINTR == errno);

        return r;
}

static void process_image(const void *p)
{
				FILE* fp;
				fp = fopen("test","w+");
        fputs(p, fp);
        fclose(fp);
      //  fflush(stdout);
}

static int read_frame(void)
{
        struct v4l2_buffer buf;
        unsigned int i;

        switch (io) {
        case IO_METHOD_READ:
                if (-1 == read(fd, buffers[0].start, buffers[0].length)) {
                        switch (errno) {
                        case EAGAIN:
                                return 0;

                        case EIO:
                                /* Could ignore EIO, see spec. */

                                /* fall through */

                        default:
                                errno_exit("read");
                        }
                }

                process_image(buffers[0].start);

                break;

        case IO_METHOD_MMAP:
                CLEAR (buf);

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

                if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
                        switch (errno) {
                        case EAGAIN:
                                return 0;

                        case EIO:
                                /* Could ignore EIO, see spec. */

                                /* fall through */

                        default:
                                errno_exit("VIDIOC_DQBUF");
                        }
                }

                assert(buf.index < n_buffers);

                process_image(buffers[buf.index].start);

                if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
                        errno_exit("VIDIOC_QBUF");

                break;

        case IO_METHOD_USERPTR:
                CLEAR(buf);

                buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
                buf.memory = V4L2_MEMORY_USERPTR;

                if (-1 == xioctl(fd, VIDIOC_DQBUF, &buf)) {
                        switch (errno) {
                        case EAGAIN:
                                return 0;

                        case EIO:
                                /* Could ignore EIO, see spec. */

                                /* fall through */

                        default:
                                errno_exit("VIDIOC_DQBUF");
                        }
                }

                for (i = 0; i < n_buffers; ++i)
                        if (buf.m.userptr == (unsigned long) buffers[i].start
                            && buf.length == buffers[i].length)
                                break;

                assert(i < n_buffers);

                process_image((void *) buf.m.userptr);

                if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
                        errno_exit("VIDIOC_QBUF");

                break;
        }

        return 1;
}

static void mainloop(void)
{
        unsigned int count;

        count = 100;

        while (count-- > 0) {
                for (;;) {
                        fd_set fds;
                        struct timeval tv;
                        int r;

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

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

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

                        if (-1 == r) {
                                if (EINTR == errno)
                                        continue;

                                errno_exit("select");
                        }

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

                        if (read_frame())
                                break;
        
                        /* EAGAIN - continue select loop. */
                }
        }
}

static void stop_capturing(void)
{
        enum v4l2_buf_type type;

        switch (io) {
        case IO_METHOD_READ:
                /* Nothing to do. */
                break;

        case IO_METHOD_MMAP:
        case IO_METHOD_USERPTR:
                type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

                if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
                        errno_exit("VIDIOC_STREAMOFF");

                break;
        }
}

static void start_capturing(void)
{
        unsigned int i;
        enum v4l2_buf_type type;

        switch (io) {
        case IO_METHOD_READ:
                /* Nothing to do. */
                break;

        case IO_METHOD_MMAP:
                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 == xioctl(fd, VIDIOC_QBUF, &buf))
                                errno_exit("VIDIOC_QBUF");
                }
                
                type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

                if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
                        errno_exit("VIDIOC_STREAMON");

                break;

        case IO_METHOD_USERPTR:
                for (i = 0; i < n_buffers; ++i) {
                        struct v4l2_buffer buf;

                        CLEAR(buf);

                        buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
                        buf.memory      = V4L2_MEMORY_USERPTR;
                        buf.index       = i;
                        buf.m.userptr   = (unsigned long) buffers[i].start;
                        buf.length      = buffers[i].length;

                        if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
                                errno_exit("VIDIOC_QBUF");
                }

                type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

                if (-1 == xioctl(fd, VIDIOC_STREAMON, &type))
                        errno_exit("VIDIOC_STREAMON");

                break;
        }
}

static void uninit_device(void)
{
        unsigned int i;

        switch (io) {
        case IO_METHOD_READ:
                free(buffers[0].start);
                break;

        case IO_METHOD_MMAP:
                for (i = 0; i < n_buffers; ++i)
                        if (-1 == munmap(buffers[i].start, buffers[i].length))
                                errno_exit("munmap");
                break;

        case IO_METHOD_USERPTR:
                for (i = 0; i < n_buffers; ++i)
                        free(buffers[i].start);
                break;
        }

        free(buffers);
}

static void init_read(unsigned int buffer_size)
{
        buffers = calloc(1, sizeof (*buffers));

        if (!buffers) {
                fprintf(stderr, "Out of memory\n");
                exit(EXIT_FAILURE);
        }

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

        if (!buffers[0].start) {
                fprintf(stderr, "Out of memory\n");
                exit(EXIT_FAILURE);
        }
}

static void init_mmap(void)
{