摄像头程序详解

来源：互联网发布：大数据专业委员会编辑：程序博客网时间：2024/05/01 18:45
程序名：usbcamera.cppMakefile：usbcamera: usbcamera.cpparm-linux-g++ usbcamera.cpp -Wall -O2 -o usbcameraarm-linux-strip -s usbcameraclean:rm usbcamera可执行文件：usbcamera 使用方法：将可执行文件下载到开发板，执行，会在当前文件夹生成一张图片。#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;/*8.出队列以取得已采集数据的帧缓冲，取得原始采集数据。VIDIOC_DQBUF*/    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/*9.将缓冲重新入队列尾,这样可以循环采集。VIDIOC_QBUF*/     ff=ioctl (fd, VIDIOC_QBUF, &buf); //再将其入列    if(ff<0)//把数据从缓存中读取出来        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-mmap.jpg", "w");//图片文件名/*1.打开设备文件。 int fd=open(”/dev/video0″,O_RDWR);*********/    fd = open (dev_name, O_RDWR /* required */ | O_NONBLOCK, 0);//打开设备/*2.取得设备的capability，看看设备具有什么功能，比如是否具有视频输入,或者音频输入输出等。VIDIOC_QUERYCAP,struct v4l2_capability*/    int ff=ioctl (fd, VIDIOC_QUERYCAP, &cap);//获取摄像头参数    if(ff<0)        printf("failture VIDIOC_QUERYCAP\n");/*3.设置视频的制式和帧格式，制式包括PAL，NTSC，帧的格式个包括宽度和高度等。*/        struct v4l2_fmtdesc fmt1;        int ret;        memset(&fmt1, 0, sizeof(fmt1));        fmt1.index = 0;        fmt1.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;    //获取当前驱动支持的视频格式        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);        }    //帧的格式，比如宽度，高度等    CLEAR (fmt);    fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE; //数据流类型，必须永远是V4L2_BUF_TYPE_VIDEO_CAPTURE    fmt.fmt.pix.width = 640;//宽，必须是16的倍数    fmt.fmt.pix.height = 480;////高，必须是16的倍数    fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_JPEG;//视频数据存储类型//V4L2_PIX_FMT_YUYV;//V4L2_PIX_FMT_YVU420;//V4L2_PIX_FMT_YUYV;    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;    //设置当前驱动的频捕获格式     ff = ioctl (fd, VIDIOC_S_FMT, &fmt);     if(ff<0)        printf("failture VIDIOC_S_FMT\n");    //计算图片大小    file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height; /*4.向驱动申请帧缓冲，一般不超过5个。struct v4l2_requestbuffers*/    struct v4l2_requestbuffers req;    CLEAR (req);    req.count = 1;//缓存数量，也就是说在缓存队列里保持多少张照片    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;    req.memory = V4L2_MEMORY_MMAP;//或V4L2_MEMORY_USERPTR    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 = (struct buffer*)calloc (req.count, sizeof (*buffers));//内存中建立对应空间/*5.将申请到的帧缓冲映射到用户空间，这样就可以直接操作采集到的帧了，而不必去复制。mmap*/    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;        //把VIDIOC_REQBUFS中分配的数据缓存转换成物理地址            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 */,buf.length,PROT_READ | PROT_WRITE /* required */,MAP_SHARED /* recommended */,fd, buf.m.offset);//通过mmap建立映射关系,返回映射区的起始地址           if (MAP_FAILED == buffers[n_buffers].start)            printf ("mmap failed\n");        }/*6.将申请到的帧缓冲全部入队列，以便存放采集到的数据.VIDIOC_QBUF,struct v4l2_buffer*/    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;            //把数据从缓存中读取出来            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;/*7.开始视频的采集。VIDIOC_STREAMON*/    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?件描述符集清空           FD_SET (fd, &fds);//在文件描述符集合中增鍔????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->start, buffers->length))            printf ("munmap error");    type = V4L2_BUF_TYPE_VIDEO_CAPTURE; /*10.停止视频的采集。VIDIOC_STREAMOFF*/        if (-1 == ioctl(fd, VIDIOC_STREAMOFF, &type))                 printf("VIDIOC_STREAMOFF");/*11.关闭视频设备。close(fd);*/    close (fd);    fclose (file_fd);    exit (EXIT_SUCCESS);    return 0;}
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