//V4L2使用示例程序//来源：网络//时间：2013.08.27 #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; //摄像头设备属性struct v4l2_format fmt; //视频捕获帧格式struct v4l2_fmtdesc fmt1;unsigned int i;enum v4l2_buf_type type; int ret;file_fd = fopen("test-mmap.jpg", "w"); //打开图片 fd = open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);//打开视频设备 int ff = ioctl (fd, VIDIOC_QUERYCAP, &cap); //获取摄像头参数if(ff<0) printf("failture VIDIOC_QUERYCAP\n"); memset(&fmt1, 0, sizeof(fmt1)); fmt1.index = 0; fmt1.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; while ((ret = ioctl(fd, VIDIOC_ENUM_FMT, &fmt1)) == 0) //获取当前支持的格式 { 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.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; 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);exit (EXIT_SUCCESS);return 0;}
