V4L2摄像头获取单幅图片测试程序（MMAP模式）

#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; ioctl (fd, VIDIOC_DQBUF, &buf); //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 ioctl (fd, VIDIOC_QBUF, &buf); //再将其入列 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-mmap.jpg", "w");//图片文件名 fd = open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);//打开设备 ioctl (fd, VIDIOC_QUERYCAP, &cap);//获取摄像头参数 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_YUYV; fmt.fmt.pix.field = V4L2_FIELD_INTERLACED; ioctl (fd, VIDIOC_S_FMT, &fmt); //设置图像格式 file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height; //计算图片大小 struct v4l2_requestbuffers req; CLEAR (req); req.count = 4; req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; req.memory = V4L2_MEMORY_MMAP; ioctl (fd, VIDIOC_REQBUFS, &req); //申请缓冲，count是申请的数量 if (req.count < 2) 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"); close (fd); fclose (file_fd); exit (EXIT_SUCCESS); return 0; }