linux下的V4L2提取USB網路攝影機映像（一）

使用了是中星微的Z301B的USB網路攝影機，在天嵌的板子上啟動並執行，在網路上搜了好久的資料，自己也做了好就，可是還是不行啊，我是沒有ARM基礎的，接觸linux也就一兩個星期多，現在真的是沒有一點頭緒了，記下來吧，計算下來以後慢慢品嘗了~~

一下的程式可以實現映像的採集，可是只能採集一張圖片，然後儲存為JPG格式的，就算我選擇的視頻格式為UYVY格式，儲存為YUV格式，但是最終檔案內部格式還是JPG格式的，因為利用YUV解碼器無法查看檔案，將尾碼改為JPG後可以用映像查看器查看··········現在我知道要在程式中提取出映像的RGB資訊，然後進行轉換，轉換為YUV格式的，但是找了好久，都沒有找到相關資料啊··········真的挺鬱悶的 ╮(╯▽╰)╭

下面是提取一張圖片的程式原始碼，已經實現了，但是程式是別人的，我想改改，將圖片儲存為YUV格式的，或者視頻也可以，但是真不知道如何下手了···經過了兩個星期的爬滾，還是一無所獲~~~~悲劇啊·························

 

/*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;}