在VMware里面调用v4l2-ctl捕获图像，或者opencv的VideoCapture(0)捕获图像，或者直接调用v4l2的函数，在streamon后，调用select读取数据，均会一直提示select timeout的问题，大概率是由于USB版本的兼容性造成的，做如下设置基本能够解决。
另外，附上一个完整的例子：
/*
* V4L2 video capture example
*
*
* This program is a plus version of program provided with the V4L2 API
*
* dotphoenix@qq.com
*
*/
#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 <stdarg.h>
#include <unistd.h>
#include <time.h>
#include <linux/videodev2.h>
//gcc -g -Wall -o capture_v4l2 capture_v4l2.c
logger//Synsynchronization is not considered///
typedef struct {
FILE * (*fopen)(char const * const filename, char const * const mode);
int (*fprintf)(FILE *fp, char const * const fmt, ...);
int (*vfprintf)(FILE *fp, char const * const fmt, va_list argp);
int (*fclose)(FILE* fp);
} std_file_t;
void std_file_init(std_file_t * const std_file) {
std_file->fopen = fopen;
std_file->fprintf = fprintf;
std_file->vfprintf = vfprintf;
std_file->fclose = fclose;
}
typedef enum {
OFF,
DEBUG,
INFO,
WARNING,
ERROR
} logger_level_t;
typedef struct {
logger_level_t level;
int write_to_file ;
FILE *fp;
std_file_t *std_file;
} logger_t;
static logger_t* logger;
static void logger_format_current_time(char* ts) {
time_t rawtime;
struct tm *info;
time( &rawtime );
info = localtime( &rawtime );
strftime(ts, 80, "%Y-%m-%d %H:%M:%S", info);
}
static const char* logger_format_level(int level) {
switch (level)
{
case DEBUG:
return "[DEBUG]";
case INFO:
return "[INFO]";
case WARNING:
return "[WARNING]";
case ERROR:
return "[ERROR]";
default:
return "[UNKNOWN]";
}
}
void logger_log(logger_level_t const level, char const * const file, size_t const line, char const * const fmt, ...) {
if (level < logger->level) {
return;
}
char ts[64] = {0};
logger_format_current_time(ts);
logger->std_file->fprintf(logger->fp, "%s %s %s: %lu: ", logger_format_level(level), ts, file, line);
va_list argp;
va_start(argp, fmt);
logger->std_file->vfprintf(logger->fp, fmt, argp);
va_end(argp);
logger->std_file->fprintf(logger->fp, "\n");
}
#define log_debug(...) logger_log(DEBUG, __FILE__, __LINE__, __VA_ARGS__)
#define log_info(...) logger_log(INFO, __FILE__, __LINE__, __VA_ARGS__)
#define log_warn(...) logger_log(WARNING, __FILE__, __LINE__, __VA_ARGS__)
#define log_error(...) logger_log(ERROR, __FILE__, __LINE__, __VA_ARGS__)
static int logger_init(
logger_level_t const level,
char const * const filename,
int const write_to_file
) {
std_file_t* std_file = (std_file_t*)malloc(sizeof(std_file_t));
logger = (logger_t*)malloc(sizeof(logger_t));
std_file_init(std_file);
logger->level = level;
logger->write_to_file = write_to_file;
logger->std_file = std_file;
if (logger->write_to_file) {
logger->fp = logger->std_file->fopen(filename, "a");
if (logger->fp == NULL) {
fprintf(stderr, "append log file %s failed, error %d, %s\n", filename, errno, strerror(errno));
return -1;
}
} else {
logger->fp = stderr;
}
char ts[128] = {0};
logger_format_current_time(ts);
strcat(ts, " start new logger -------------------\n");
log_warn(ts);
return 0;
}
void logger_uninit() {
if(logger == NULL) {
return;
}
if(logger->write_to_file) {
if(logger->fp != NULL) {
logger->std_file->fclose(logger->fp);
logger->fp = NULL;
}
}
free(logger->std_file);
free(logger);
}
//
#define CLEAR(x) memset(&(x), 0, sizeof(x))
enum io_method_t {
IO_METHOD_READ,
IO_METHOD_MMAP,
IO_METHOD_USERPTR,
};
struct buffer_t {
void *start;
size_t length;
};
static char *dev_name;
static enum io_method_t io_method = IO_METHOD_MMAP;
static int fd = -1;
struct buffer_t *buffers;
static unsigned int n_buffers;
static int save_to_file = 1; //save to file
static int force_format_yuyv = 1; //force to use yuyv format
static int force_format_mjpeg = 0;//force to use mjpeg
static int frame_count = 30 * 2; //total save frame count
static int req_width = 640;
static int req_height = 480;
static int req_rate_numerator = 30;
static int req_rate_denominator = 1;
static int frame_index = 0;
static void errno_exit(const char *s)
{
fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno));
log_error("%s error %d, %s\n", s, errno, strerror(errno));
logger_uninit();
exit(EXIT_FAILURE);
}
static void general_exit_v(char const * const fmt, ...)
{
char msg[512] = {0};
va_list argp;
va_start(argp, fmt);
vsprintf(msg, fmt, argp);
va_end(argp);
strcat(msg, "\n");
fprintf(stderr, "%s", msg);
log_error(msg);
logger_uninit();
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 generate_save_to_fullpath(char* fullpath, const char*postfix, int file_index)
{
char cwd[256] = {0};
getcwd(cwd, 255);
sprintf(fullpath, "%s/pictures/%06d.%s", cwd, file_index, postfix);
}
static void process_image(const void *p, int size)
{
frame_index++;
//mark one frame on the console
fprintf(stderr, ".");
fflush(stderr);
if(save_to_file == 1) {
char fullpath[128] = {0};
if(force_format_mjpeg == 1) {
generate_save_to_fullpath(fullpath, "jpg", frame_index);
}
else {
generate_save_to_fullpath(fullpath, "yuyv", frame_index);
}
FILE *fp = fopen(fullpath, "wb");
if(fp == NULL) {
fprintf(stderr, "create file failed, file %s, error %d, %s\n", fullpath, errno, strerror(errno));
log_error("create file failed, file %s, error %d, %s\n", fullpath, errno, strerror(errno));
return;
} else {
fwrite(p, size, 1, fp);
fflush(fp);
fclose(fp);
log_debug("one frame coming and save to file, size=%d, path=%s \n", size, fullpath);
}
}
else {
log_debug("one frame coming and not save to file, size=%d \n", size);
}
}
static int read_frame(void)
{
struct v4l2_buffer buf;
unsigned int i;
switch (io_method) {
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, buffers[0].length);
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, buf.bytesused);
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, buf.bytesused);
if (-1 == xioctl(fd, VIDIOC_QBUF, &buf))
errno_exit("VIDIOC_QBUF");
break;
}
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 = 30;
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) {
general_exit_v("select timeout");
}
if (read_frame())
break;
/* EAGAIN - continue select loop. */
}
}
}
static void stop_capturing(void)
{
enum v4l2_buf_type type;
switch (io_method) {
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_method) {
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");
log_info("%s stream on", dev_name);
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");
log_info("%s stream on", dev_name);
break;
}
}
static void uninit_device(void)
{
unsigned int i;
switch (io_method) {
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) {
general_exit_v("Out of memory");
}
buffers[0].length = buffer_size;
buffers[0].start = malloc(buffer_size);
if (!buffers[0].start) {
general_exit_v("Out of memory");
}
log_info("initialize read&write method of %s successfully");
}
static void init_mmap(void)
{
struct v4l2_requestbuffers req;
CLEAR(req);
req.count = 8;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
if (-1 == xioctl(fd, VIDIOC_REQBUFS, &req)) {
if (EINVAL == errno) {
general_exit_v("%s does not support "
"memory mappingn", dev_name);
} else {
errno_exit("VIDIOC_REQBUFS");
}
}
if (req.count < 2) {
general_exit_v("Insufficient buffer_t memory on %s", dev_name);
}
buffers = calloc(req.count, sizeof(*buffers));
if (!buffers) {
general_exit_v("Out of memory");
}
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");
}
log_info("initialize mmap method of %s successfully", dev_name);
}
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) {
general_exit_v("%s does not support user pointer i/o", dev_name);
} else {
errno_exit("VIDIOC_REQBUFS");
}
}
buffers = calloc(4, sizeof(*buffers));
if (!buffers) {
general_exit_v("Out of memory");
}
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) {
general_exit_v("Out of memory");
}
}
log_info("initialize userp method of %s successfully", dev_name);
}
static int check_fmt(int fd, __u32 fmt)
{
struct v4l2_format v4l2_fmt;
CLEAR(v4l2_fmt);
v4l2_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (ioctl (fd, VIDIOC_G_FMT, &v4l2_fmt) == -1) {
log_error("ERROR camera VIDIOC_G_FMT Failed.");
return -1;
}
if (v4l2_fmt.fmt.pix.pixelformat == fmt) {
return 1;
}
else {
log_error("ERROR camera VIDIOC_S_FMT Failed, %u vs %u.", v4l2_fmt.fmt.pix.pixelformat, fmt);
return -1;
}
}
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) {
general_exit_v("%s is no V4L2 device", dev_name);
} else {
errno_exit("VIDIOC_QUERYCAP");
}
}
if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
general_exit_v("%s is no video capture device",
dev_name);
}
switch (io_method) {
case IO_METHOD_READ:
if (!(cap.capabilities & V4L2_CAP_READWRITE)) {
general_exit_v("%s does not support read i/o",
dev_name);
}
log_info("%s supports read and write", dev_name);
break;
case IO_METHOD_MMAP:
case IO_METHOD_USERPTR:
if (!(cap.capabilities & V4L2_CAP_STREAMING)) {
general_exit_v("%s does not support streaming i/o",
dev_name);
}
log_info("%s supports streaming", dev_name);
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(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) {
struct v4l2_fract *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) {
log_error( "the driver changed the time per frame from "
"%d/%d to %d/%d failed",
req_rate_denominator, req_rate_numerator,
tpf->numerator, tpf->denominator);
}
else {
log_info( "the driver changed the time per frame from "
"%d/%d to %d/%d successfully",
req_rate_denominator, req_rate_numerator,
tpf->numerator, tpf->denominator);
}
}
else {
log_error("the driver does not allow to change time per frame");
}
CLEAR(fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (force_format_yuyv) {
fmt.fmt.pix.width = req_width;
fmt.fmt.pix.height = req_height;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.field = V4L2_FIELD_ANY;
if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
errno_exit("VIDIOC_S_FMT");
assert(check_fmt(fd, V4L2_PIX_FMT_YUYV) == 1);
log_info("set format of %s to %u successfully", dev_name, fmt.fmt.pix.pixelformat);
/* Note VIDIOC_S_FMT may change width and height. */
} else if (force_format_mjpeg) {
fmt.fmt.pix.width = req_width;
fmt.fmt.pix.height = req_height;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
fmt.fmt.pix.field = V4L2_FIELD_ANY;
if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt))
errno_exit("VIDIOC_S_FMT");
assert(check_fmt(fd, V4L2_PIX_FMT_MJPEG) == 1);
log_info("set format of %s to %u successfully", dev_name, fmt.fmt.pix.pixelformat);
/* 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");
log_info("format of %s is %u ", dev_name, fmt.fmt.pix.pixelformat);
}
/* 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_method) {
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)) {
general_exit_v("Cannot identify device '%s': %d, %s",
dev_name, errno, strerror(errno));
}
if (!S_ISCHR(st.st_mode)) {
general_exit_v("%s is no device", dev_name);
}
fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);
if (-1 == fd) {
general_exit_v("Cannot open '%s': %d, %s",
dev_name, errno, strerror(errno));
}
else {
log_info("Open device %s successfully.", dev_name);
}
}
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 messagen"
"-m | --mmap Use memory mapped buffers [default]n"
"-r | --read Use read() callsn"
"-u | --userp Use application allocated buffersn"
"-s | --save Save stream to file"
"-f | --format Force format to 640x480 YUYVn"
"-c | --count Number of frames to grab [%i]n"
"",
argv[0], dev_name, frame_count);
}
static const char short_options[] = "d:hmruofc:";
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' },
{ "save", no_argument, NULL, 's' },
{ "format", no_argument, NULL, 'f' },
{ "count", required_argument, NULL, 'c' },
{ 0, 0, 0, 0 }
};
int main(int argc, char **argv)
{
dev_name = "/dev/video0";
char log_filename[256] = {0};
char cwd[256] = {0};
getcwd(cwd, 255);
sprintf(log_filename, "%s/v4l2_log.txt", cwd);
logger_init(DEBUG, log_filename, 1);
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 'm':
io_method = IO_METHOD_MMAP;
break;
case 'r':
io_method = IO_METHOD_READ;
break;
case 'u':
io_method = IO_METHOD_USERPTR;
break;
case 's':
save_to_file = 1;
break;
case 'j':
force_format_mjpeg = 1;
break;
case 'n':
force_format_yuyv = 1;
break;
case 'y':
errno = 0;
frame_count = strtol(optarg, NULL, 0);
if (errno)
errno_exit(optarg);
break;
default:
usage(stderr, argc, argv);
exit(EXIT_FAILURE);
}
}
open_device();
init_device();
start_capturing();
mainloop();
stop_capturing();
uninit_device();
close_device();
logger_uninit(&logger);
return 0;
}
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