v4l2captureexample.c

V4L2 Specification 配套源码

/*
* 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)
{
	struct v4l2_requestbuffers req;
	CLEAR (req);
	req.count = 4;
	req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_MMAP;
	if (-1 == xioctl (fd, VIDIOC_REQBUFS, &req)) {
		if (EINVAL == errno) {
			fprintf (stderr, "%s does not support "
				"memory mapping\n", dev_name);
			exit (EXIT_FAILURE);
		} else {
			errno_exit ("VIDIOC_REQBUFS");
		}
	}
	if (req.count < 2) {
		fprintf (stderr, "Insufficient buffer memory on %s\n",
			dev_name);
		exit (EXIT_FAILURE);
	}
	buffers = calloc (req.count, sizeof (*buffers));
	if (!buffers) {
		fprintf (stderr, "Out of memory\n");
		exit (EXIT_FAILURE);
	}
	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) {
		struct v4l2_buffer buf;
		CLEAR (buf);
		buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		buf.memory = V4L2_MEMORY_MMAP;
		buf.index = n_buffers;
		if (-1 == xioctl (fd, VIDIOC_QUERYBUF, &buf))
			errno_exit ("VIDIOC_QUERYBUF");
		buffers[n_buffers].length = buf.length;
		buffers[n_buffers].start =
			mmap (NULL /* start anywhere */,
			buf.length,
			PROT_READ | PROT_WRITE /* required */,
			MAP_SHARED /* recommended */,
			fd, buf.m.offset);
		if (MAP_FAILED == buffers[n_buffers].start)
			errno_exit ("mmap");
	}
}

static void
init_userp (unsigned int buffer_size)
{
	struct v4l2_requestbuffers req;
	unsigned int page_size;
	page_size = getpagesize ();
	buffer_size = (buffer_size + page_size - 1) & ~(page_size - 1);
	CLEAR (req);
	req.count = 4;
	req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	req.memory = V4L2_MEMORY_USERPTR;
	if (-1 == xioctl (fd, VIDIOC_REQBUFS, &req)) {
		if (EINVAL == errno) {
			fprintf (stderr, "%s does not support "
				"user pointer i/o\n", dev_name);
			exit (EXIT_FAILURE);
		} else {
			errno_exit ("VIDIOC_REQBUFS");
		}
	}
	buffers = calloc (4, sizeof (*buffers));
	if (!buffers) {
		fprintf (stderr, "Out of memory\n");
		exit (EXIT_FAILURE);
	}
	for (n_buffers = 0; n_buffers < 4; ++n_buffers) {
		buffers[n_buffers].length = buffer_size;
		buffers[n_buffers].start = memalign (/* boundary */ page_size,
			buffer_size);
		if (!buffers[n_buffers].start) {
			fprintf (stderr, "Out of memory\n");
			exit (EXIT_FAILURE);
		}
	}
}
static void
init_device (void)
{
	struct v4l2_capability cap;
	struct v4l2_cropcap cropcap;
	struct v4l2_crop crop;
	struct v4l2_format fmt;
	unsigned int min;
	if (-1 == xioctl (fd, VIDIOC_QUERYCAP, &cap)) {
		if (EINVAL == errno) {
			fprintf (stderr, "%s is no V4L2 device\n",

				dev_name);
			exit (EXIT_FAILURE);
		} else {
			errno_exit ("VIDIOC_QUERYCAP");
		}
	}
	if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
		fprintf (stderr, "%s is no video capture device\n",
			dev_name);
		exit (EXIT_FAILURE);
	}
	switch (io) {
case IO_METHOD_READ:
	if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
		fprintf (stderr, "%s does not support read i/o\n",
			dev_name);
		exit (EXIT_FAILURE);
	}
	break;
case IO_METHOD_MMAP:
case IO_METHOD_USERPTR:
	if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
		fprintf (stderr, "%s does not support streaming i/o\n",
			dev_name);
		exit (EXIT_FAILURE);
	}
	break;
	}
	/* Select video input, video standard and tune here. */
	CLEAR (cropcap);
	cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
	if (0 == xioctl (fd, VIDIOC_CROPCAP, &cropcap)) {
		crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
		crop.c = cropcap.defrect; /* reset to default */
		if (-1 == xioctl (fd, VIDIOC_S_CROP, &crop)) {
			switch (errno) {
case EINVAL:
	/* Cropping not supported. */
	break;
default:
	/* Errors ignored. */
	break;
			}
		}
	} else {



		/* Errors ignored. */
	}
	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;
	if (-1 == xioctl (fd, VIDIOC_S_FMT, &fmt))
		errno_exit ("VIDIOC_S_FMT");
	/* Note VIDIOC_S_FMT may change width and height. */
	/* Buggy driver paranoia. */
	min = fmt.fmt.pix.width * 2;
	if (fmt.fmt.pix.bytesperline < min)
		fmt.fmt.pix.bytesperline = min;
	min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
	if (fmt.fmt.pix.sizeimage < min)
		fmt.fmt.pix.sizeimage = min;
	switch (io) {
case IO_METHOD_READ:
	init_read (fmt.fmt.pix.sizeimage);
	break;
case IO_METHOD_MMAP:
	init_mmap ();
	break;
case IO_METHOD_USERPTR:
	init_userp (fmt.fmt.pix.sizeimage);
	break;
	}
}
static void
close_device (void)
{
	if (-1 == close (fd))
		errno_exit ("close");
	fd = -1;
}
static void
open_device (void)
{
	struct stat st;
	if (-1 == stat (dev_name, &st)) {
		fprintf (stderr, "Cannot identify ’%s’: %d, %s\n",
			dev_name, errno, strerror (errno));



		exit (EXIT_FAILURE);
	}
	if (!S_ISCHR (st.st_mode)) {
		fprintf (stderr, "%s is no device\n", dev_name);
		exit (EXIT_FAILURE);
	}
	fd = open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);
	if (-1 == fd) {
		fprintf (stderr, "Cannot open ’%s’: %d, %s\n",
			dev_name, errno, strerror (errno));
		exit (EXIT_FAILURE);
	}
}
static void
usage (FILE * fp,
	   int argc,
	   char ** argv)
{
	fprintf (fp,
		"Usage: %s [options]\n\n"
		"Options:\n"
		"-d | --device name Video device name [/dev/video]\n"
		"-h | --help Print this message\n"
		"-m | --mmap Use memory mapped buffers\n"
		"-r | --read Use read() calls\n"
		"-u | --userp Use application allocated buffers\n"
		"",
		argv[0]);
}
static const char short_options [] = "d:hmru";
static const struct option
long_options [] = {
	{"device", required_argument, NULL,'d'},
	{"help", no_argument, NULL,'h'},
	{"mmap", no_argument, NULL,'m'},
	{"read", no_argument, NULL,'r'},
	{"userp", no_argument, NULL,'u'},
	{0, 0, 0, 0}
};
int
main (int argc,
	  char ** argv)
{
	dev_name = "/dev/video0";
	for (;;) {
		int index;
		int c;
		c = getopt_long (argc, argv,

			short_options, long_options,
			&index);
		if (-1 == c)
			break;
		switch (c) {
case 0: /* getopt_long() flag */
	break;
case 'd':
	dev_name = optarg;
	break;
case 'h':
	usage (stdout, argc, argv);
	exit (EXIT_SUCCESS);
case 'm':
	io = IO_METHOD_MMAP;
	break;
case 'r':
	io = IO_METHOD_READ;
	break;
case 'u':
	io = IO_METHOD_USERPTR;
	break;
default:
	usage (stderr, argc, argv);
	exit (EXIT_FAILURE);
		}
	}
	open_device ();
	init_device ();
	start_capturing ();
	mainloop ();
	stop_capturing ();
	uninit_device ();
	close_device ();
	exit (EXIT_SUCCESS);
	return 0;
}