linux下的V4L2提取USB摄像头图像（一）

使用了是中星微的Z301B的USB摄像头，在天嵌的板子上运行的，在网络上搜了好久的资料，自己也做了好就，可是还是不行啊，我是没有ARM基础的，接触linux也就一两个星期多，现在真的是没有一点头绪了，记下来吧，计算下来以后慢慢品尝了~~

一下的程序可以实现图像的采集，可是只能采集一张图片，然后保存为JPG格式的，就算我选择的视频格式为UYVY格式，保存为YUV格式，但是最终文件内部格式还是JPG格式的，因为利用YUV解码器无法查看文件，将后缀改为JPG后可以用图像查看器查看··········现在我知道要在程序中提取出图像的RGB信息，然后进行转换，转换为YUV格式的，但是找了好久，都没有找到相关资料啊··········真的挺郁闷的 ╮(╯▽╰)╭

下面是提取一张图片的程序源代码，已经实现了，但是程序是别人的，我想改改，将图片保存为YUV格式的，或者视频也可以，但是真不知道如何下手了···经过了两个星期的爬滚，还是一无所获~~~~悲剧啊·························

/*arm-linux-gcc -o usbcamera usbcamera.c ; then download the file and put in the /sbin .*/
#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 CAPTURE_FILE "/media/frame.yuv"
#define CLEAR(x) memset (&(x), 0, sizeof (x))

struct buffer {
        void * start;
        size_t length;
};

static char * dev_name = "/dev/video0";
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;

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"); 
    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);

///////////////////////
    FILE *fp = fopen(CAPTURE_FILE, "w+");
    if (fp < 0) {
        printf("open frame data file failed\n");
        return -1;
    }
    fwrite(buffers[buf.index].start, 1, buffers[buf.index].length, fp);

fclose(fp);
    printf("Capture one frame saved in %s\n", CAPTURE_FILE);
////////////////////
    ff=ioctl (fd, VIDIOC_QBUF, &buf); 
    if(ff<0)
        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");


    fd = open (dev_name, O_RDWR | O_NONBLOCK, 0);

    int ff=ioctl (fd, VIDIOC_QUERYCAP, &cap);
    if(ff<0)
        printf("failture VIDIOC_QUERYCAP\n");


 // Print capability infomations
    printf("Capability Informations:\n");
    printf(" driver: %s\n", cap.driver);
    printf(" card: %s\n", cap.card);
    printf(" bus_info: %s\n", cap.bus_info);
    printf(" version: %08X\n", cap.version);
    printf(" capabilities: %08X\n", cap.capabilities);




        struct v4l2_fmtdesc fmt1;
        int ret;
        memset(&fmt1, 0, sizeof(fmt1));
        fmt1.index = 0;
        fmt1.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    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);
        }

    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_UYVY;//V4L2_PIX_FMT_JPEG;
    fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;

    ff = ioctl (fd, VIDIOC_S_FMT, &fmt); 
    if(ff<0)
        printf("failture VIDIOC_S_FMT\n");

    file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height; 


    struct v4l2_requestbuffers req;
    CLEAR (req);
    req.count = 4;//1
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;
    ff = ioctl (fd, VIDIOC_REQBUFS, &req); 
 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));


    for (n_buffers = 0; 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 (-1 == ioctl (fd, VIDIOC_QUERYBUF, &buf)) 
                printf ("VIDIOC_QUERYBUF error\n");

           buffers[n_buffers].length = buf.length;

           buffers[n_buffers].start = mmap (NULL ,buf.length,PROT_READ | PROT_WRITE ,MAP_SHARED ,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))
                printf ("VIDIOC_QBUF failed\n");
    }

    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (-1 == ioctl (fd, VIDIOC_STREAMON, &type)) 

           printf ("VIDIOC_STREAMON failed\n");



    for (;;) 

    {

           fd_set fds;
           struct timeval tv;

           int r;
           FD_ZERO (&fds);
           FD_SET (fd, &fds);
           tv.tv_sec = 2;
           tv.tv_usec = 0;



r = select (fd + 1, &fds, NULL, NULL, &tv);
        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 ())
               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; 
       if (-1 == ioctl(fd, VIDIOC_STREAMOFF, &type)) 
                printf("VIDIOC_STREAMOFF");
   close (fd);
    fclose (file_fd);
    exit (EXIT_SUCCESS);
    return 0;
}