linux下摄像头图像数据的获取

2.6.32内核，V4L2架构

亲自测试可用

在友善之臂MINI2440开发板上测试可用

源程序如下

[cpp]  view plain copy

 <span style="font-size:18px;">#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";//摄像头设备名
 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;
 //////////////////////////////////////////////////////
 //获取一帧数据
 //////////////////////////////////////////////////////
 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"); //出列采集的帧缓冲

     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); //将其写入文件中

     ff=ioctl (fd, VIDIOC_QBUF, &buf); //再将其入列
     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");                 //图片文件名

     fd = open (dev_name, O_RDWR /* required */ |O_NONBLOCK);//打开设备
     if(fd<0)
     {
         perror("open faiure!");
         exit(1);
     }
     int ff=ioctl (fd, VIDIOC_QUERYCAP, &cap);               //获取摄像头参数
     if(ff<0)
         printf("failture VIDIOC_QUERYCAP\n");

     struct v4l2_fmtdesc fmt1;
     int ret;
     memset(&fmt1, 0, sizeof(fmt1));
     fmt1.index = 0;            //初始化为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); //设置图像格式
     if(ff<0)
         printf("failture VIDIOC_S_FMT\n");
     file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height; //计算图片大小

     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); //申请缓冲，count是申请的数量
     if(ff<0)
         printf("failture VIDIOC_REQBUFS\n");
     if (req.count < 1)
         printf("Insufficient buffer memory\n");

     buffers = calloc (req.count, sizeof (*buffers));//内存中建立对应空间

     for (n_buffers = 0; n_buffers < req.count; ++n_buffers)
     {
         struct v4l2_buffer buf;   //驱动中的一帧
         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)) //映射用户空间
             printf ("VIDIOC_QUERYBUF error\n");

         buffers[n_buffers].length = buf.length;
         buffers[n_buffers].start =
         mmap (NULL /* start anywhere */,    //通过mmap建立映射关系
             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))//申请到的缓冲进入列队
             printf ("VIDIOC_QBUF failed\n");
     }

     type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

     if (-1 == ioctl (fd, VIDIOC_STREAMON, &type)) //开始捕捉图像数据
         printf ("VIDIOC_STREAMON failed\n");

     for (;;) //这一段涉及到异步IO
     {
         fd_set fds;
         struct timeval tv;
         int r;

         FD_ZERO (&fds);//将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个新的文件描述符

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

         r = select (fd + 1, &fds, NULL, NULL, &tv);//判断是否可读（即摄像头是否准备好），tv是定时

         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 ())//如果可读，执行read_frame ()函数，并跳出循环
             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;
 }</span>