capture.c

video for linux,example

/*
 *  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)
{
        fputc ('.', stdout);
        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)
{