Linux下面實現視頻捕獲

/*
* 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 <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 EI
/* 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 EI
/* 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 EI
/* 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.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;

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 = malloc (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/video";

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;
}