最近想做一个  使用 video4linux2（注意不是 video4linux ）采集 usb 摄像头上的图像的程序，网上找了一个源码，运行成功，分享过程。

程序编译时直接使用 gcc -o test test.c就可以了。

本人运行时所带参数：./test -r 2

运行所生成的jpg图像文件：

程序源代码：

/*
  *  V4L2 video capture example
  */ 
  
 #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 <asm/types.h>       /* for videodev2.h */ 
  
 #include <linux/videodev2.h> 
  
 #define CLEAR(x) memset (&(x), 0, sizeof (x)) 
  
 typedef enum 
 { 
   IO_METHOD_READ, 
   IO_METHOD_MMAP, 
   IO_METHOD_USERPTR, 
 } io_method; 
  
 struct buffer 
 { 
   void *start; 
   size_t length; 
 }; 
  
 static char *dev_name = NULL; 
 static io_method io = IO_METHOD_MMAP; 
     /* can be V4L2_PIX_FMT_YUV420 or V4L2_PIX_FMT_PWC2 */ 
 static int pixel_format = V4L2_PIX_FMT_YUV420; 
 static int fd = -1; 
 struct buffer *buffers = NULL; 
 static unsigned int n_buffers = 0; 
 static unsigned int width = 320; 
 static unsigned int height = 240; 
 static unsigned int count = 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 fd, int request, void *arg) 
 { 
   int r; 
  
   do 
     r = ioctl(fd, request, arg); 
   while (-1 == r && EINTR == errno); 
  
   return r; 
 } 
  
 static void process_image(const void *p, ssize_t size) 
 { 


unsigned char *bbuf=(unsigned char *)p;

int ll;  
 for ( ll= 1024 ; ll< 60000; ll++) if ((bbuf[ll] == 0xFF) && (bbuf[ll+1] == 0xD9)) break;

FILE *fp2;
fp2=fopen("xx.jpg","w");
fwrite(bbuf, 1, ll+2, fp2);

 

/*
   static int no_image = 0; 
   char filename[1024]; 
   int fd; 
   ssize_t written = 0; 
  
   snprintf(filename, sizeof(filename), "/tmp/webcam-%5.5d.%s", 
        no_image++, pixel_format == V4L2_PIX_FMT_YUV420 ? "yuv" : "raw"); 
  
   fd = open(filename, O_CREAT | O_WRONLY | O_TRUNC, S_IRUSR | S_IWUSR); 
   if (fd < 0) 
     { 
       fputc('*', stdout); 
       fflush(stdout); 
       return; 
     } 
   do 
     { 
       int ret; 
       ret = write(fd, p + written, size - written); 
       if (ret < 0) 
     { 
       fputc('+', stdout); 
       fflush(stdout); 
       return; 
     } 
       written += ret; 
     } 
   while (written < size); 
   close(fd); 
  
   fputc('.', stdout); 
   fflush(stdout); 

*/
 } 
  
 static int read_frame(void) 
 { 
   struct v4l2_buffer buf; 
   unsigned int i; 
   ssize_t read_bytes; 
   unsigned int total_read_bytes; 
  
   switch (io) 
     { 
     case IO_METHOD_READ: 
       total_read_bytes = 0; 
       do 
        { 
      read_bytes = read(fd, buffers[0].start, buffers[0].length); 
      if (read_bytes < 0) 
       { 
         switch (errno) 
          { 
           case EIO: 
           case EAGAIN: 
         continue; 
           default: 
         errno_exit("read"); 
          } 
       } 
      total_read_bytes += read_bytes; 
  
        } while (total_read_bytes < buffers[0].length); 
       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.length); 
  
       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.length); 
  
       if (-1 == xioctl(fd, VIDIOC_QBUF, &buf)) 
     errno_exit("VIDIOC_QBUF"); 
  
       break; 
     } 
  
   return 1; 
 } 
  
 static void mainloop(void) 
 { 
   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; 
  
   switch (io) 
     { 
     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) 
     { 
     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"); 
  
       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.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"); 
  
       break; 
     } 
 } 
  
 static void uninit_device(void) 
 { 
   unsigned int i; 
  
   switch (io) 
     { 
     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) 
     { 
       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 = 1; 
   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_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) 
     { 
       fprintf(stderr, "%s does not support " 
           "user pointer i/o/n", dev_name); 
       exit(EXIT_FAILURE); 
     } 
       else 
     { 
       errno_exit("VIDIOC_REQBUFS"); 
     } 
     } 
  
   buffers = calloc(4, sizeof(*buffers)); 
  
   if (!buffers) 
     { 
       fprintf(stderr, "Out of memory/n"); 
       exit(EXIT_FAILURE); 
     } 
  
   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) 
     { 
       fprintf(stderr, "Out of memory/n"); 
       exit(EXIT_FAILURE); 
     } 
     } 
 } 
  
 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"); 
     } 

     } 
   //VIDIOC_QUERYCAP,VIDIOC_S_CROP,VIDIOC_CROPCAP
   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. */ 
  
   cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
  
   if (-1 == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) 
     { 
       /* Errors ignored. */ 
     } 
  
   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; 
     } 
     } 
  
   CLEAR(fmt); 
  
   fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; 
   fmt.fmt.pix.width = width; 
   fmt.fmt.pix.height = height; 
   fmt.fmt.pix.pixelformat = pixel_format; 
   fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; 
  
printf("%d  %d /n",width,height);
   if (-1 == xioctl(fd, VIDIOC_S_FMT, &fmt)) 
     errno_exit("VIDIOC_S_FMT"); 
  
   /* Note VIDIOC_S_FMT may change width and height. */ 
   width = fmt.fmt.pix.width; 
   height = fmt.fmt.pix.height; 
   printf("%d  %d /n",width,height);
   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); 
     } 
 }  
 

 int main(int argc, char **argv) 
 { 
   dev_name = "/dev/video0"; 
  

printf("%d,%d,%d/n",VIDIOC_QUERYCAP,VIDIOC_S_CROP,VIDIOC_CROPCAP);
    open_device(); 
  
   init_device(); 
  
   start_capturing(); 
  
   mainloop(); 
  
   stop_capturing(); 
  
   uninit_device(); 
  
   close_device(); 
  
   exit(EXIT_SUCCESS); 
  
   return 0; 
 } 

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