V4L2总结（3）代码示例

//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(ff0) 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 ffioctl (fd, VIDIOC_QBUF, buf); //再将其入列 if(ff0) {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(ff0) 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(ff0) 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(ff0) 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; }