关于v4l2视频采集应用问题

linyongzhounan 2011-07-18 10:45:12

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_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;
}[/code]

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