어떻게 v4L을 캡처하는 USB 웹 캠 (640x480)에 대한 프로그램을

Question

에 USB 웹캠 드라이버를 설치 한 다음 V4L을 사용하여 캡처하고 싶습니다. 회신 해주세요. 웹캠을 사용하여 캡처하는 프로그램을 작성할 수 있습니다.

Answer 1

linuxTV (http://linuxtv.org/downloads/v4l-dvb-apis/)의 참조를 사용하여 V4l에서 작업합니다. 그들은 V4l과 몇 가지 예제에 대한 문서를 가지고 있습니다. 다음 예제를 보자 (linuxTV에서 얻음) :

#include <stdio.h> 
#include <stdlib.h> 
#include <string.h> 
#include <fcntl.h> 
#include <errno.h> 
#include <sys/ioctl.h> 
#include <sys/types.h> 
#include <sys/time.h> 
#include <sys/mman.h> 
#include <linux/videodev2.h> 
#include "../libv4l/include/libv4l2.h" 

#define CLEAR(x) memset(&(x), 0, sizeof(x)) 

struct buffer { 
     void *start; 
     size_t length; 
}; 

static void xioctl(int fh, int request, void *arg) 
{ 
     int r; 

     do { 
       r = v4l2_ioctl(fh, request, arg); 
     } while (r == -1 && ((errno == EINTR) || (errno == EAGAIN))); 

     if (r == -1) { 
       fprintf(stderr, "error %d, %s\n", errno, strerror(errno)); 
       exit(EXIT_FAILURE); 
     } 
} 

int main(int argc, char **argv) 
{ 
     struct v4l2_format    fmt; 
     struct v4l2_buffer    buf; 
     struct v4l2_requestbuffers  req; 
     enum v4l2_buf_type    type; 
     fd_set       fds; 
     struct timeval     tv; 
     int        r, fd = -1; 
     unsigned int     i, n_buffers; 
     char       *dev_name = "/dev/video0"; 
     char       out_name[256]; 
     FILE       *fout; 
     struct buffer     *buffers; 

     fd = v4l2_open(dev_name, O_RDWR | O_NONBLOCK, 0); 
     if (fd < 0) { 
       perror("Cannot open device"); 
       exit(EXIT_FAILURE); 
     } 

     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_RGB24; 
     fmt.fmt.pix.field  = V4L2_FIELD_INTERLACED; 
     xioctl(fd, VIDIOC_S_FMT, &fmt); 
     if (fmt.fmt.pix.pixelformat != V4L2_PIX_FMT_RGB24) { 
       printf("Libv4l didn't accept RGB24 format. Can't proceed.\n"); 
       exit(EXIT_FAILURE); 
     } 
     if ((fmt.fmt.pix.width != 640) || (fmt.fmt.pix.height != 480)) 
       printf("Warning: driver is sending image at %dx%d\n", 
         fmt.fmt.pix.width, fmt.fmt.pix.height); 

     CLEAR(req); 
     req.count = 2; 
     req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
     req.memory = V4L2_MEMORY_MMAP; 
     xioctl(fd, VIDIOC_REQBUFS, &req); 

     buffers = calloc(req.count, sizeof(*buffers)); 
     for (n_buffers = 0; n_buffers < req.count; ++n_buffers) { 
       CLEAR(buf); 

       buf.type  = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
       buf.memory  = V4L2_MEMORY_MMAP; 
       buf.index  = n_buffers; 

       xioctl(fd, VIDIOC_QUERYBUF, &buf); 

       buffers[n_buffers].length = buf.length; 
       buffers[n_buffers].start = v4l2_mmap(NULL, buf.length, 
           PROT_READ | PROT_WRITE, MAP_SHARED, 
           fd, buf.m.offset); 

       if (MAP_FAILED == buffers[n_buffers].start) { 
         perror("mmap"); 
         exit(EXIT_FAILURE); 
       } 
     } 

     for (i = 0; i < n_buffers; ++i) { 
       CLEAR(buf); 
       buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
       buf.memory = V4L2_MEMORY_MMAP; 
       buf.index = i; 
       xioctl(fd, VIDIOC_QBUF, &buf); 
     } 
     type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 

     xioctl(fd, VIDIOC_STREAMON, &type); 
     for (i = 0; i < 20; i++) { 
       do { 
         FD_ZERO(&fds); 
         FD_SET(fd, &fds); 

         /* Timeout. */ 
         tv.tv_sec = 2; 
         tv.tv_usec = 0; 

         r = select(fd + 1, &fds, NULL, NULL, &tv); 
       } while ((r == -1 && (errno = EINTR))); 
       if (r == -1) { 
         perror("select"); 
         return errno; 
       } 

       CLEAR(buf); 
       buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
       buf.memory = V4L2_MEMORY_MMAP; 
       xioctl(fd, VIDIOC_DQBUF, &buf); 

       sprintf(out_name, "out%03d.ppm", i); 
       fout = fopen(out_name, "w"); 
       if (!fout) { 
         perror("Cannot open image"); 
         exit(EXIT_FAILURE); 
       } 
       fprintf(fout, "P6\n%d %d 255\n", 
         fmt.fmt.pix.width, fmt.fmt.pix.height); 
       fwrite(buffers[buf.index].start, buf.bytesused, 1, fout); 
       fclose(fout); 

       xioctl(fd, VIDIOC_QBUF, &buf); 
     } 

     type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
     xioctl(fd, VIDIOC_STREAMOFF, &type); 
     for (i = 0; i < n_buffers; ++i) 
       v4l2_munmap(buffers[i].start, buffers[i].length); 
     v4l2_close(fd); 

     return 0; 
}