struct v4l2_format 解析 （二）

v4l2_format 解析，在内核中这么定义的

1598   struct v4l2_format {
1599          enum v4l2_buf_type type;
1600          union {
1601                   struct v4l2_pix_format          pix;     /* V4L2_BUF_TYPE_VIDEO_CAPTURE */
1602                   struct v4l2_window              win;     /* V4L2_BUF_TYPE_VIDEO_OVERLAY */
1603                   struct v4l2_vbi_format          vbi;     /* V4L2_BUF_TYPE_VBI_CAPTURE */
1604                   struct v4l2_sliced_vbi_format   sliced;  /* V4L2_BUF_TYPE_SLICED_VBI_CAPTURE */
1605                   __u8    raw_data[200];                   /* user-defined */
1606           } fmt;
1607   };
1608

struct v4l2_pix_format 定义：

270    struct v4l2_pix_format {
 271            __u32                   width;
 272            __u32                   height;
 273            __u32                   pixelformat;
 274             enum v4l2_field         field;
 275            __u32                   bytesperline;   /* for padding, zero if unused */
 276             __u32                   sizeimage;
 277            enum v4l2_colorspace    colorspace;
 278            __u32                   priv;           /* private data, depends on pixelformat */
 279   };

在程序中，这么写的：

CLEAR (fmt);
fmt.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width       = 320;
fmt.fmt.pix.height      = 240;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_YUYV;
fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;
ioctl (fd, VIDIOC_S_FMT, &fmt); //设置图像格式

printf("v4l2_buf_type(CAPTURE=1)    :%d\n",fmt.type);  /* CAPTURE=1*/
printf("width                    :%d\n",fmt.fmt.pix.width);
printf("height                   :%d\n",fmt.fmt.pix.height);
printf("pixel'yuyv'                :%d\n",('Y'|'U'<<8|'Y'<<16|'V'<<24));
printf("pixel'jpeg'             :%d\n",('J'|'P'<<8|'E'<<16|'G'<<24));
printf("pixelformat              :%d\n",fmt.fmt.pix.pixelformat);
printf("v4l1_filed(FIELD_INTERCACED=4)  :%d\n",fmt.fmt.pix.field);
printf("bytesperline                :%d\n",fmt.fmt.pix.bytesperline);
printf("sizeimage                :%d\n",fmt.fmt.pix.sizeimage);
printf("colorspace(COLOSPACE_JPEG=7)    :%d\n",fmt.fmt.pix.colorspace);
printf("priv                    :%d\n",fmt.fmt.pix.priv);

v4l2_buf_type(CAPTURE=1)               :1
width                                                    :320
height                                                  :240
pixel'yuyv'                                        :1448695129
pixel'jpeg'                                         :1195724874  ##得出 zc3xx 的输出是 JPEG格式，这里自动修改的格式
pixelformat                                        :1195724874
v4l1_filed(FIELD_INTERCACED=4)   :1          ###
bytesperline                                      :320
sizeimage                                            :29390        图像大小？？？？
colorspace(COLOSPACE_JPEG=7)       :7
priv                                                      :1

pixel'jpeg'                     :1195724874
pixelformat                     :1195724874

  我们原先设置的是 V4L2_PIX_FMT_YUYV，但是这里和我们设置的不一样， 这里设备自动修改为 JPEG格式，说明，zc3xx输出的JPEG格式

v4l1_filed(FIELD_INTERCACED=4)  :1

this device has no fields ：说明这个设备没有 场设置
 filed 定义如下：

106   enum v4l2_field {
 107               V4L2_FIELD_ANY           = 0, /* driver can choose from none,
 108                                                                      top, bottom, interlaced
 
109                              depending on whatever it thinks
 110                                                                      is approximate ... */
 111               V4L2_FIELD_NONE          = 1, /* this device has no fields ... */
 112              V4L2_FIELD_TOP           = 2, /* top field only */
 113              V4L2_FIELD_BOTTOM        = 3, /* bottom field only */
 114              V4L2_FIELD_INTERLACED    = 4, /* both fields interlaced */
 115              V4L2_FIELD_SEQ_TB        = 5, /* both fields sequential into one
 116                                                                           buffer, top-bottom order */
 117              V4L2_FIELD_SEQ_BT        = 6, /* same as above + bottom-top order */
 118              V4L2_FIELD_ALTERNATE     = 7, /* both fields alternating into
 119                                                                              separate buffers */
 120              V4L2_FIELD_INTERLACED_TB = 8, /* both fields interlaced, top field
 121                                                                                first and the top field is
 122                                                                                transmitted first */
 123              V4L2_FIELD_INTERLACED_BT = 9, /* both fields interlaced, top field
 124                                                                                 first and the bottom field is
 125                                                                                      transmitted first */
 126     };

bytesperline                    :320

bytesPerLine 表明缓冲区中有多少字节用于表示图像中一行像素的所有

像素值。由于一个像素可能有多个字节表示，所以 bytesPerLine 可能是

字段 width 值的若干倍


表示 一行像素点，有320个字节表示

sizeimage                       :       29390   ？？？？？

colorspace(COLOSPACE_JPEG=7)    :7

       /* I know there will be cameras that send this.  So, this is
 204           * unspecified chromaticities and full 0-255 on each of the
 205            * Y'CbCr components
 206            */
       未指定色度，充分0-255对每个* Y'CbCr组件
 207        V4L2_COLORSPACE_JPEG          = 7,

注意：如果该视频设备驱动不支持你所设定的图像格式，视频驱动会重新修改struct v4l2_format结构体变量的值为该视频设备所支持的图像格式，所以在程序设计中，设定完所有的视频格式后，要获取实际的视频格式，要重新读取struct v4l2_format结构体变量。