v4l2采集视频和图片源码

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 #include <assert.h>

 #include <getopt.h>             /* getopt_long() */

 #include <fcntl.h>              /* low-level i/o */
 #include <unistd.h>
 #include <errno.h>
 #include <sys/stat.h>
 #include <sys/types.h>
 #include <sys/time.h>
 #include <sys/mman.h>
 #include <sys/ioctl.h>

 #include <linux/videodev2.h>

 #define FORCED_WIDTH  640
 #define FORCED_HEIGHT 480
 #define FORCED_FORMAT V4L2_PIX_FMT_YUYV
 #define FORCED_FIELD  V4L2_FIELD_ANY

 static int verbose = ;
 #define pr_debug(fmt, arg...) \
     if (verbose) fprintf(stderr, fmt, ##arg)

 #define CLEAR(x) memset(&(x), 0, sizeof(x)) //相当于CLEAR(x) =memset(&(x), 0, sizeof(x))

 enum io_method {                           //枚举，即只能取其中的一个值。也是一种数据结构
     IO_METHOD_READ,
     IO_METHOD_MMAP,
     IO_METHOD_USERPTR,
 };

 struct buffer {
     void   *start;
     size_t  length;                    //size_t =unsigned int 用来表示sizeof的
 };

 static char            *dev_name;         //用来保存设备名
 static enum io_method   io = IO_METHOD_MMAP;
 static int              fd = -;
 struct buffer          *buffers;
 static unsigned int     n_buffers;
 static int        out_buf;
 static int              force_format;
 static int              frame_count = ;
 static char             *video_name="video.yuv";
     FILE *fp; //保存视频

 static void errno_exit(const char *s)
 {
     fprintf(stderr, "%s error %d, %s\n", s, errno, strerror(errno));
     exit(EXIT_FAILURE);
 }

 static int xioctl(int fh, int request, void *arg)
 {
     int r;

     do {
         r = ioctl(fh, request, arg);
     } while (- == r && EINTR == errno);

     return r;
 }

 static void process_image(const void *p, int size)
 {
     pr_debug("%s: called!\n", __func__);
          //采集视频
         fwrite(p,size,,fp);//如果要查看采集视频的格式，在linux下可以通过安装v4l-utils,然后执行v4l2-ctl --all来查看视频采集的相关信息
             // 保存为一张张图片
       /*     FILE *fp;
     static int num = 1;
     char picture_name[20];

     sprintf(picture_name,"picture%d.jpg",num ++);

     if((fp = fopen(picture_name,"w")) == NULL)
     {
         perror("Fail to fopen");
         exit(EXIT_FAILURE);
     }

     fwrite(p,size,1,fp);
     usleep(500);

     fclose(fp);
                                  */

               // 打印到标准输出
     /*if (out_buf)
         fwrite(p, size, 1, stdout);

     fflush(stderr);
     fprintf(stderr, ".");
     fflush(stdout);
                            */

 }

 static int read_frame(void)
 {
     struct v4l2_buffer buf;
     unsigned int i;

     pr_debug("%s: called!\n", __func__);

     switch (io) {
     case IO_METHOD_READ:

         break;

     case IO_METHOD_MMAP:
         CLEAR(buf);

         buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
         buf.memory = V4L2_MEMORY_MMAP;

         if (- == xioctl(fd, VIDIOC_DQBUF, &buf)) {
             switch (errno) {
             case EAGAIN:
                 return ;

             case EIO:
                 /* Could ignore EIO, see spec. */

                 /* fall through */

             default:
                 errno_exit("VIDIOC_DQBUF");
             }
         }

         assert(buf.index < n_buffers);

         process_image(buffers[buf.index].start, buf.bytesused);

         if (- == xioctl(fd, VIDIOC_QBUF, &buf))
             errno_exit("VIDIOC_QBUF");
         break;

     case IO_METHOD_USERPTR:

         break;
     }

     return ;
 }

 static void mainloop(void)
 {
     unsigned int count;

     pr_debug("%s: called!\n", __func__);

     count = frame_count;

     while (count-- > ) {
         for (;;) {
             fd_set fds;
             struct timeval tv;
             int r;

             FD_ZERO(&fds);
             FD_SET(fd, &fds);

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

             r = select(fd + , &fds, NULL, NULL, &tv);

             if (- == r) {
                 if (EINTR == errno)
                     continue;
                 errno_exit("select");
             }

             if ( == r) {
                 fprintf(stderr, "select timeout\n");
                 exit(EXIT_FAILURE);
             }

             if (read_frame())
                 break;
             /* EAGAIN - continue select loop. */
         }
     }
 }

 static void stop_capturing(void)
 {
     enum v4l2_buf_type type;

     pr_debug("%s: called!\n", __func__);

     switch (io) {
     case IO_METHOD_READ:
         /* Nothing to do. */
         break;

     case IO_METHOD_MMAP: //会执行下面的
     case IO_METHOD_USERPTR:
         type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
         if (- == xioctl(fd, VIDIOC_STREAMOFF, &type))
             errno_exit("VIDIOC_STREAMOFF");
         break;
     }
 }

 static void start_capturing(void)
 {
     unsigned int i;
     enum v4l2_buf_type type;
     int err;

     pr_debug("%s: called!\n", __func__);

     pr_debug("\tn_buffers: %d\n", n_buffers);

     switch (io) {
     case IO_METHOD_READ:
         /* Nothing to do. */
         break;

     case IO_METHOD_MMAP:
         for (i = ; i < n_buffers; ++i) {
             struct v4l2_buffer buf;

             pr_debug("\ti: %d\n", i);

             CLEAR(buf);
             buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
             buf.memory = V4L2_MEMORY_MMAP;
             buf.index = i;

             pr_debug("\tbuf.index: %d\n", buf.index);

             err == xioctl(fd, VIDIOC_QBUF, &buf);
             pr_debug("\terr: %d\n", err);

             if (- == err)
                 errno_exit("VIDIOC_QBUF");

             pr_debug("\tbuffer queued!\n");
         }

         pr_debug("Before STREAMON\n");
         type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
         if (- == xioctl(fd, VIDIOC_STREAMON, &type))
             errno_exit("VIDIOC_STREAMON");
         pr_debug("After STREAMON\n");
         break;

     case IO_METHOD_USERPTR:

         break;
     }
 }

 static void uninit_device(void)
 {
     unsigned int i;

     pr_debug("%s: called!\n", __func__);

     switch (io) {
     case IO_METHOD_READ:
         free(buffers[].start);
         break;

     case IO_METHOD_MMAP:
         for (i = ; i < n_buffers; ++i)
             if (- == munmap(buffers[i].start, buffers[i].length))
                 errno_exit("munmap");
         break;

     case IO_METHOD_USERPTR:
         for (i = ; i < n_buffers; ++i)
             free(buffers[i].start);
         break;
     }

     free(buffers);
 }

 static void init_read(unsigned int buffer_size)
 {
     pr_debug("%s: called!\n", __func__);

     buffers = calloc(, sizeof(*buffers));

     if (!buffers) {
         fprintf(stderr, "Out of memory\n");
         exit(EXIT_FAILURE);
     }

     buffers[].length = buffer_size;
     buffers[].start = malloc(buffer_size);

     if (!buffers[].start) {
         fprintf(stderr, "Out of memory\n");
         exit(EXIT_FAILURE);
     }
 }

 static void init_mmap(void)  //（3）
 {
     struct v4l2_requestbuffers req;

     pr_debug("%s: called!\n", __func__);

     CLEAR(req);

     req.count = ;
     req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
     req.memory = V4L2_MEMORY_MMAP;

     if (- == xioctl(fd, VIDIOC_REQBUFS, &req)) {
         if (EINVAL == errno) {
             fprintf(stderr, "%s does not support "
                  "memory mapping\n", dev_name);
             exit(EXIT_FAILURE);
         } else {
             errno_exit("VIDIOC_REQBUFS");
         }
     }
     pr_debug("\treq.count: %d\n", req.count);
     pr_debug("\treq.type: %d\n", req.type);
     pr_debug("\treq.memory: %d\n", req.memory);
     pr_debug("\n");

     if (req.count < ) {
         fprintf(stderr, "Insufficient buffer memory on %s\n",
              dev_name);
         exit(EXIT_FAILURE);
     }

     buffers = calloc(req.count, sizeof(*buffers));

     if (!buffers) {
         fprintf(stderr, "Out of memory\n");
         exit(EXIT_FAILURE);
     }

     for (n_buffers = ; n_buffers < req.count; ++n_buffers) {
         struct v4l2_buffer buf;

         CLEAR(buf);

         buf.type        = V4L2_BUF_TYPE_VIDEO_CAPTURE;
         buf.memory      = V4L2_MEMORY_MMAP;
         buf.index       = n_buffers;

         if (- == xioctl(fd, VIDIOC_QUERYBUF, &buf))
             errno_exit("VIDIOC_QUERYBUF");

         pr_debug("\tbuf.index: %d\n", buf.index);
         pr_debug("\tbuf.type: %d\n", buf.type);
         pr_debug("\tbuf.bytesused: %d\n", buf.bytesused);
         pr_debug("\tbuf.flags: %d\n", buf.flags);
         pr_debug("\tbuf.field: %d\n", buf.field);
         pr_debug("\tbuf.timestamp.tv_sec: %ld\n", (long) buf.timestamp.tv_sec);
         pr_debug("\tbuf.timestamp.tv_usec: %ld\n", (long) buf.timestamp.tv_usec);
         pr_debug("\tbuf.timecode.type: %d\n", buf.timecode.type);
         pr_debug("\tbuf.timecode.flags: %d\n", buf.timecode.flags);
         pr_debug("\tbuf.timecode.frames: %d\n", buf.timecode.frames);
         pr_debug("\tbuf.timecode.seconds: %d\n", buf.timecode.seconds);
         pr_debug("\tbuf.timecode.minutes: %d\n", buf.timecode.minutes);
         pr_debug("\tbuf.timecode.hours: %d\n", buf.timecode.hours);
         pr_debug("\tbuf.timecode.userbits: %d,%d,%d,%d\n",
                 buf.timecode.userbits[],
                 buf.timecode.userbits[],
                 buf.timecode.userbits[],
                 buf.timecode.userbits[]);
         pr_debug("\tbuf.sequence: %d\n", buf.sequence);
         pr_debug("\tbuf.memory: %d\n", buf.memory);
         pr_debug("\tbuf.m.offset: %d\n", buf.m.offset);
         pr_debug("\tbuf.length: %d\n", buf.length);
         pr_debug("\tbuf.input: %d\n", buf.input);
         pr_debug("\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);

         if (MAP_FAILED == buffers[n_buffers].start)
             errno_exit("mmap");
     }
 }

 static void init_device(void) //static表示次函数只能在本文件中调用
 {
     struct v4l2_capability cap;
     struct v4l2_cropcap cropcap;
     struct v4l2_crop crop;
     struct v4l2_format fmt;
     unsigned int min;

     pr_debug("%s: called!\n", __func__);

     if (- == xioctl(fd, VIDIOC_QUERYCAP, &cap)) {
         if (EINVAL == errno) {
             fprintf(stderr, "%s is no V4L2 device\n",
                  dev_name);
             exit(EXIT_FAILURE);
         } else {
             errno_exit("VIDIOC_QUERYCAP");
         }
     }

     pr_debug("\tdriver: %s\n"
          "\tcard: %s \n"
          "\tbus_info: %s\n",
             cap.driver, cap.card, cap.bus_info);
     pr_debug("\tversion: %u.%u.%u\n",
             (cap.version >> ) & 0xFF,
             (cap.version >> ) & 0xFF,
             cap.version & 0xFF);
     pr_debug("\tcapabilities: 0x%08x\n", cap.capabilities);

     if (!(cap.capabilities & V4L2_CAP_VIDEO_CAPTURE)) {
         fprintf(stderr, "%s is no video capture device\n",
              dev_name);
         exit(EXIT_FAILURE);
     }

     /* Select video input, video standard and tune here. */

     CLEAR(cropcap);

     cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

     if ( == xioctl(fd, VIDIOC_CROPCAP, &cropcap)) {
         pr_debug("\tcropcap.type: %d\n", cropcap.type);
         pr_debug("\tcropcap.bounds.left: %d\n", cropcap.bounds.left);
         pr_debug("\tcropcap.bounds.top: %d\n", cropcap.bounds.top);
         pr_debug("\tcropcap.bounds.width: %d\n", cropcap.bounds.width);
         pr_debug("\tcropcap.bounds.height: %d\n", cropcap.bounds.height);

         pr_debug("\tcropcap.defrect.left: %d\n", cropcap.defrect.left);
         pr_debug("\tcropcap.defrect.top: %d\n", cropcap.defrect.top);
         pr_debug("\tcropcap.defrect.width: %d\n", cropcap.defrect.width);
         pr_debug("\tcropcap.defrect.height: %d\n", cropcap.defrect.height);

         pr_debug("\tcropcap.pixelaspect.numerator: %d\n", cropcap.pixelaspect.numerator);
         pr_debug("\tcropcap.pixelaspect.denominator: %d\n", cropcap.pixelaspect.denominator);
         pr_debug("\n");

         CLEAR(crop);
         crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
         crop.c = cropcap.defrect; /* reset to default */

         if (- == xioctl(fd, VIDIOC_S_CROP, &crop)) {
             switch (errno) {
             case EINVAL:
                 /* Cropping not supported. */
                 break;
             default:
                 /* Errors ignored. */
                 pr_debug("\tcropping not supported\n");
                 break;
             }
         }
     } else {
         /* Errors ignored. */
     }

     CLEAR(fmt);

     fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
     if (force_format) {
         fmt.fmt.pix.width       = FORCED_WIDTH;
         fmt.fmt.pix.height      = FORCED_HEIGHT;
         fmt.fmt.pix.pixelformat = FORCED_FORMAT;
         fmt.fmt.pix.field       = FORCED_FIELD;

         pr_debug("\tfmt.fmt.pix.pixelformat: %c,%c,%c,%c\n",
                 fmt.fmt.pix.pixelformat & 0xFF,
                 (fmt.fmt.pix.pixelformat >> ) & 0xFF,
                 (fmt.fmt.pix.pixelformat >> ) & 0xFF,
                 (fmt.fmt.pix.pixelformat >> ) & 0xFF
                 );
         pr_debug("\n");

         if (- == xioctl(fd, VIDIOC_S_FMT, &fmt))
             errno_exit("VIDIOC_S_FMT");

         /* Note VIDIOC_S_FMT may change width and height. */
     } else {
         /* Preserve original settings as set by v4l2-ctl for example */
         if (- == xioctl(fd, VIDIOC_G_FMT, &fmt))
             errno_exit("VIDIOC_G_FMT");

         fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
         pr_debug("\tfmt.fmt.pix.pixelformat: %c,%c,%c,%c\n",
                 fmt.fmt.pix.pixelformat & 0xFF,
                 (fmt.fmt.pix.pixelformat >> ) & 0xFF,
                 (fmt.fmt.pix.pixelformat >> ) & 0xFF,
                 (fmt.fmt.pix.pixelformat >> ) & 0xFF
                 );

     }

     /* Buggy driver paranoia. */
     min = fmt.fmt.pix.width * ;
     if (fmt.fmt.pix.bytesperline < min)
         fmt.fmt.pix.bytesperline = min;
     min = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height;
     if (fmt.fmt.pix.sizeimage < min)
         fmt.fmt.pix.sizeimage = min;

     switch (io) {
     case IO_METHOD_READ:
         init_read(fmt.fmt.pix.sizeimage);
         break;

     case IO_METHOD_MMAP:
         init_mmap();
         break;

     case IO_METHOD_USERPTR:

         break;
     }
 }

 static void close_device(void)
 {
     pr_debug("%s: called!\n", __func__);

     if (- == close(fd))//==可以防止你写成=（相当与赋值）这样条件始终成立
         errno_exit("close");

     fd = -;
 }

 static void open_device(void)//
 {
     struct stat st;

     pr_debug("%s: called!\n", __func__);//_func_表示此时在那个函数里面

     if (- == stat(dev_name, &st)) {//获取文件信息
         fprintf(stderr, "Cannot identify '%s': %d, %s\n",
              dev_name, errno, strerror(errno));
         exit(EXIT_FAILURE);//非正常退出 EXIT_FAILURE=1， EXIT_SUCCSES=0 正常退出
     }

     if (!S_ISCHR(st.st_mode)) {
         fprintf(stderr, "%s is no device\n", dev_name);
         exit(EXIT_FAILURE);
     }

     fd = open(dev_name, O_RDWR /* required */ | O_NONBLOCK, );//非阻塞模式打开文件

     if (- == fd) {
         fprintf(stderr, "Cannot open '%s': %d, %s\n",
              dev_name, errno, strerror(errno));
         exit(EXIT_FAILURE);
     }
 }

 static void usage(FILE *fp, int argc, char **argv)
 {
     fprintf(fp,
          "Usage: %s [options]\n\n"
          "Version 1.3\n"
          "Options:\n"
          "-d | --device name   Video device name [%s]\n"
          "-h | --help          Print this message\n"
          "-m | --mmap          Use memory mapped buffers [default]\n"
          "-r | --read          Use read() calls\n"
          "-u | --userp         Use application allocated buffers\n"
          "-o | --output        Outputs stream to stdout\n"
          "-f | --format        Force format to 640x480 YUYV\n"
          "-c | --count         Number of frames to grab [%i]\n"
          "-v | --verbose       Verbose output\n"
          "",
          argv[], dev_name, frame_count);
 }
 //关于命令解析见百度getopt-long；
 static const char short_options[] = "d:hmruofc:v";// 短选项 ：表示带参数

 static const struct option //长选项
 long_options[] = {
     { "device", required_argument, NULL, 'd' },
     { "help",   no_argument,       NULL, 'h' },
     { "mmap",   no_argument,       NULL, 'm' },
     { "read",   no_argument,       NULL, 'r' },
     { "userp",  no_argument,       NULL, 'u' },
     { "output", no_argument,       NULL, 'o' },
     { "format", no_argument,       NULL, 'f' },
     { "count",  required_argument, NULL, 'c' },
     { "verbose", no_argument,      NULL, 'v' },
     { , , ,  }
 };

 int main(int argc, char **argv)
 {
     dev_name = "/dev/video0";

     for (;;) {
         int idx;
         int c;

         c = getopt_long(argc, argv,
                 short_options, long_options, &idx);

         if (- == c)
             break;

         switch (c) {
         case : /* getopt_long() flag */
             break;

         case 'd':
             dev_name = optarg;
             break;

         case 'h':
             usage(stdout, argc, argv);
             exit(EXIT_SUCCESS);

         case 'm':
             io = IO_METHOD_MMAP;
             break;

         case 'r':
             io = IO_METHOD_READ;
             break;

         case 'u':
             io = IO_METHOD_USERPTR;
             break;

         case 'o':
             out_buf++;
             break;

         case 'f':
             force_format++;
             break;

         case 'c':
             errno = ;
             frame_count = strtol(optarg, NULL, );
             if (errno)
                 errno_exit(optarg);
             break;

         case 'v':
             verbose = ;
             break;

         default:
             usage(stderr, argc, argv);
             exit(EXIT_FAILURE);
         }
     }

 if((fp = fopen(video_name,"wa+")) == NULL)
     {
         perror("Fail to fopen");
         exit(EXIT_FAILURE);
     }

     open_device();
     init_device();
     start_capturing();
     mainloop();
     stop_capturing();
     uninit_device();
     close_device();
     fprintf(stderr, "\n");
     return ;
 }