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Last active September 28, 2023 14:22
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v4l2 capture example
/*
* V4L2 video capture example
*
* This program can be used and distributed without restrictions.
*
* This program is provided with the V4L2 API
* see http://linuxtv.org/docs.php for more information
*
* To build:
* g++ -std=c++11 -o v4l2-capture v4l2-capture.cpp
*/
#include <iostream>
#include <vector>
#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 <linux/limits.h>
#include <linux/videodev2.h>
using namespace std;
#define CLEAR(x) memset(&(x), 0, sizeof(x))
struct buffer_t {
void *start;
size_t length;
};
static const char *dev_name;
static int fd = -1;
static vector<buffer_t> buffers;
static int frame_count = 200;
static int frame_number = 0;
static string output_name;
static int req_width = 0;
static int req_height = 0;
static int req_format = V4L2_PIX_FMT_YUYV; // yuy2
static int req_rate_numerator = 60;
static int req_rate_denominator = 1;
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 fh, int request, void *arg)
{
int r;
do {
r = ioctl(fh, request, arg);
} while (-1 == r && EINTR == errno);
return r;
}
static void process_image(const void *p, int size)
{
frame_number++;
char filename[PATH_MAX];
snprintf(filename, PATH_MAX-1, output_name.c_str(), frame_number);
FILE *fp = fopen(filename,"wb");
if (fp) {
fwrite(p, size, 1, fp);
fflush(fp);
fclose(fp);
} else {
errno_exit("process_image");
}
}
static int read_frame(void)
{
struct v4l2_buffer buf;
unsigned int i;
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 < buffers.size());
process_image(buffers[buf.index].start, buf.bytesused);
if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");
return 1;
}
static void mainloop(void)
{
unsigned int count;
count = frame_count;
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;
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == xioctl(fd, VIDIOC_STREAMOFF, &type))
errno_exit("VIDIOC_STREAMOFF");
}
static void start_capturing(void)
{
unsigned int i;
enum v4l2_buf_type type;
for (i = 0; i < buffers.size(); ++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");
}
static void uninit_device(void)
{
unsigned int i;
for (i = 0; i < buffers.size(); ++i)
if (-1 == munmap(buffers[i].start, buffers[i].length))
errno_exit("munmap");
buffers.clear();
}
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.resize(req.count);
for (size_t idx = 0; idx < buffers.size(); ++idx) {
struct v4l2_buffer buf;
CLEAR(buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = idx;
if (-1 == xioctl(fd, VIDIOC_QUERYBUF, &buf))
errno_exit("VIDIOC_QUERYBUF");
buffers[idx].length = buf.length;
buffers[idx].start =
mmap(nullptr /* start anywhere */,
buf.length,
PROT_READ | PROT_WRITE /* required */,
MAP_SHARED /* recommended */,
fd, buf.m.offset);
if (MAP_FAILED == buffers[idx].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;
struct v4l2_streamparm streamparm;
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);
}
if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
fprintf(stderr, "%s does not support streaming i/o\n",
dev_name);
exit(EXIT_FAILURE);
}
/* Select video input, video standard and tune here. */
#if 0
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. */
}
#endif
CLEAR(streamparm);
streamparm.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == xioctl(fd, VIDIOC_G_PARM, &streamparm))
errno_exit("VIDIOC_G_PARM");
if (streamparm.parm.capture.capability & V4L2_CAP_TIMEPERFRAME) {
auto &tpf = streamparm.parm.capture.timeperframe;
// Swap numerator and denominator: rate is an inverted frame time :-)
tpf.numerator = req_rate_denominator;
tpf.denominator = req_rate_numerator;
if (-1 == xioctl(fd, VIDIOC_S_PARM, &streamparm))
errno_exit("VIDIOC_S_PARM");
if (tpf.numerator != req_rate_denominator ||
tpf.denominator != req_rate_numerator) {
fprintf(stderr,
"the driver changed the time per frame from "
"%d/%d to %d/%d\n",
req_rate_denominator, req_rate_numerator,
tpf.numerator, tpf.denominator);
}
} else {
fprintf(stderr, "the driver does not allow to change time per frame\n");
}
CLEAR(fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (true) {
fmt.fmt.pix.width = req_width; //replace
fmt.fmt.pix.height = req_height; //replace
fmt.fmt.pix.pixelformat = req_format; //replace
fmt.fmt.pix.field = V4L2_FIELD_ANY;
if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
errno_exit("VIDIOC_S_FMT");
/* Note VIDIOC_S_FMT may change width and height. */
} else {
/* Preserve original settings as set by v4l2-ctl for example */
if (-1 == xioctl(fd, VIDIOC_G_FMT, &fmt))
errno_exit("VIDIOC_G_FMT");
}
/* 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;
// Last step, init buffers
init_mmap();
}
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"
"Version 1.3\n"
"Options:\n"
"-d | --device name Video device name [%s]\n"
"-h | --help Print this message\n"
"-s | --size size Video size in format WIDTHxHEIGHT\n"
"-f | --format format 'yuy2' [default] or 'nv12'\n"
"-r | --rate rate Setup frame rate [60]\n"
"-o | --output output Outputs stream to stdout, format string is supported\n"
"-c | --count count Number of frames to grab [%i]\n"
"",
argv[0], dev_name, frame_count);
}
static const char short_options[] = "d:ho:f:s:c:r:";
static const struct option
long_options[] = {
{ "device", required_argument, nullptr, 'd' },
{ "help", no_argument, nullptr, 'h' },
{ "size", required_argument, nullptr, 's' },
{ "format", required_argument, nullptr, 'f' },
{ "rate", required_argument, nullptr, 'r' },
{ "output", required_argument, nullptr, 'o' },
{ "count", required_argument, nullptr, 'c' },
{ 0, 0, 0, 0 }
};
int main(int argc, char **argv)
{
dev_name = "/dev/video0";
for (;;) {
int idx;
int c;
c = getopt_long(argc, argv,
short_options, long_options, &idx);
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 'o':
output_name = optarg;
break;
case 'f':
if (strcmp(optarg, "yuy2") == 0) {
req_format = V4L2_PIX_FMT_YUYV;
} else if (strcmp(optarg, "nv12") == 0) {
req_format = V4L2_PIX_FMT_NV12;
} else {
fprintf(stderr, "Unknown format: %s\n", optarg);
exit(EXIT_FAILURE);
}
break;
case 's':
{
errno = 0;
char *endptr = nullptr;
req_width = strtol(optarg, &endptr, 10);
if (errno)
errno_exit(optarg);
if (*endptr == '\0') {
fprintf(stderr, "unknown size: %s\n", optarg);
exit(EXIT_FAILURE);
}
errno = 0;
req_height = strtol(endptr+1, nullptr, 10);
if (errno)
errno_exit(optarg);
break;
}
case 'r':
{
errno = 0;
char *endptr = nullptr;
req_rate_numerator = strtol(optarg, &endptr, 0);
if (errno)
errno_exit(optarg);
if (*endptr == '\0') {
req_rate_denominator = 1;
} else {
errno = 0;
req_rate_denominator = strtol(endptr+1, nullptr, 10);
if (errno)
errno_exit(optarg);
}
break;
}
case 'c':
errno = 0;
frame_count = strtol(optarg, nullptr, 0);
if (errno)
errno_exit(optarg);
break;
default:
usage(stderr, argc, argv);
exit(EXIT_FAILURE);
}
}
fprintf(stdout,
"device: %s\n"
"output: %s\n"
"size: %dx%d\n"
"rate: %d/%d\n",
dev_name,
output_name.c_str(),
req_width, req_height,
req_rate_numerator, req_rate_denominator);
bool invalid = false;
if (!req_width || !req_height) {
fprintf(stderr, "size can't be zero\n");
invalid = true;
}
if (!req_rate_denominator || !req_rate_numerator) {
fprintf(stderr, "rate can't be zero\n");
invalid = true;
}
if (output_name.empty()) {
fprintf(stderr, "output_name can't be empty\n");
invalid = true;
}
if (invalid)
exit(EXIT_FAILURE);
open_device();
init_device();
start_capturing();
mainloop();
stop_capturing();
uninit_device();
close_device();
fprintf(stderr, "\n");
return 0;
}
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