Linux 2.6.32內核，V4L2架構
親自測試可用
在友善之臂MINI2440開發板上測試可用
源程序如下
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
#include <getopt.h>
#include <fcntl.h>
#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>
#include <linux/videodev2.h>
#define CLEAR(x) memset (&(x), 0, sizeof (x))
struct buffer {
void * start;
size_t length;
};
static char * dev_name = "/dev/video0";//攝像頭設備名
static int fd = -1;
struct buffer * buffers = NULL;
static unsigned int n_buffers = 0;
FILE *file_fd;
static unsigned long file_length;
static unsigned char *file_name;
//////////////////////////////////////////////////////
//獲取一幀數據
//////////////////////////////////////////////////////
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;
int ff = ioctl (fd, VIDIOC_DQBUF, &buf);
if(ff<0)
printf("failture\n"); //出列采集的幀緩沖
assert (buf.index < n_buffers);
printf ("buf.index dq is %d,\n",buf.index);
fwrite(buffers[buf.index].start, buffers[buf.index].length, 1, file_fd); //將其寫入文件中
ff=ioctl (fd, VIDIOC_QBUF, &buf); //再將其入列
if(ff<0)
printf("failture VIDIOC_QBUF\n");
return 1;
}
int main (int argc,char ** argv)
{
struct v4l2_capability cap;
struct v4l2_format fmt;
unsigned int i;
enum v4l2_buf_type type;
file_fd = fopen("test.jpg", "wb"); //圖片文件名
fd = open (dev_name, O_RDWR /* required */ |O_NONBLOCK);//打開設備
if(fd<0)
{
perror("open faiure!");
exit(1);
}
int ff=ioctl (fd, VIDIOC_QUERYCAP, &cap); //獲取攝像頭參數
if(ff<0)
printf("failture VIDIOC_QUERYCAP\n");
struct v4l2_fmtdesc fmt1;
int ret;
memset(&fmt1, 0, sizeof(fmt1));
fmt1.index = 0; //初始化為0
fmt1.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
while ((ret = ioctl(fd, VIDIOC_ENUM_FMT, &fmt1)) == 0)
{
fmt1.index++;
printf("{ pixelformat = '%c%c%c%c', description = '%s' }\n",fmt1.pixelformat & 0xFF,
(fmt1.pixelformat >> 8) & 0xFF,(fmt1.pixelformat >> 16) & 0xFF,
(fmt1.pixelformat >> 24) & 0xFF,fmt1.description);
}
CLEAR (fmt);
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
// fmt.fmt.pix.width = 640;
// fmt.fmt.pix.height = 480;
fmt.fmt.pix.width = 320;
fmt.fmt.pix.height = 240;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_JPEG;//V4L2_PIX_FMT_YUYV;//V4L2_PIX_FMT_YVU420;//V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
ff = ioctl (fd, VIDIOC_S_FMT, &fmt); //設置圖像格式
if(ff<0)
printf("failture VIDIOC_S_FMT\n");
file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height; //計算圖片大小
struct v4l2_requestbuffers req;
CLEAR (req);
req.count = 1;
req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
req.memory = V4L2_MEMORY_MMAP;
ff=ioctl (fd, VIDIOC_REQBUFS, &req); //申請緩沖，count是申請的數量
if(ff<0)
printf("failture VIDIOC_REQBUFS\n");
if (req.count < 1)
printf("Insufficient buffer memory\n");
buffers = calloc (req.count, sizeof (*buffers));//內存中建立對應空間
for (n_buffers = 0; n_buffers < req.count; ++n_buffers)
{
struct v4l2_buffer buf; //驅動中的一幀
CLEAR (buf);
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = n_buffers;
if (-1 == ioctl (fd, VIDIOC_QUERYBUF, &buf)) //映射用戶空間
printf ("VIDIOC_QUERYBUF error\n");
buffers[n_buffers].length = buf.length;
buffers[n_buffers].start =
mmap (NULL /* start anywhere */, //通過mmap建立映射關系
buf.length,
PROT_READ | PROT_WRITE /* required */,
MAP_SHARED /* recommended */,
fd, buf.m.offset);
if (MAP_FAILED == buffers[n_buffers].start)
printf ("mmap failed\n");
}
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 == ioctl (fd, VIDIOC_QBUF, &buf))//申請到的緩沖進入列隊
printf ("VIDIOC_QBUF failed\n");
}
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == ioctl (fd, VIDIOC_STREAMON, &type)) //開始捕捉圖像數據
printf ("VIDIOC_STREAMON failed\n");
for (;;) //這一段涉及到異步IO
{
fd_set fds;
struct timeval tv;
int r;
FD_ZERO (&fds);//將指定的文件描述符集清空
FD_SET (fd, &fds);//在文件描述符集合中增加一個新的文件描述符
/* Timeout. */
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select (fd + 1, &fds, NULL, NULL, &tv);//判斷是否可讀（即攝像頭是否准備好），tv是定時
if (-1 == r)
{
if (EINTR == errno)
continue;
printf ("select err\n");
}
if (0 == r)
{
fprintf (stderr, "select timeout\n");
exit (EXIT_FAILURE);
}
if (read_frame ())//如果可讀，執行read_frame ()函數，並跳出循環
break;
}
unmap:
for (i = 0; i < n_buffers; ++i)
if (-1 == munmap (buffers[i].start, buffers[i].length))
printf ("munmap error");
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (-1 == ioctl(fd, VIDIOC_STREAMOFF, &type))
printf("VIDIOC_STREAMOFF");
close (fd);
fclose (file_fd);
return 0;
}