c 查询v4l2 各种参数

 
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/videodev2.h>
#include <string.h>
#include <sys/mman.h>
#include <sys/time.h>
 
int main(void) {
	int fd = open("/dev/video0", O_RDWR);
	struct v4l2_capability {  // VIDIOC_QUERYCAP
		__u8	driver[16];     //uvc
		__u8	card[32];
		__u8	bus_info[32];
		__u32   version;
		__u32	capabilities;    //功能
		__u32	device_caps;
		__u32	reserved[3];
	};
	struct v4l2_capability  cap;
	int t = ioctl(fd, VIDIOC_QUERYCAP, &cap);
	if (t < 0) {
		puts("cap error");
	}
	printf("%s\n", cap.driver);
	printf("%s\n", cap.card);
	printf("%s\n", cap.bus_info);
	printf("%d\n", cap.version);
	printf("%x\n", cap.capabilities);       //84a00001   1：视频输入卡 
	printf("%x\n", cap.device_caps);        //4200001
	printf("%d\n", cap.reserved[0]);
	printf("%d\n", cap.reserved[1]);
	printf("%d\n", cap.reserved[2]);
	puts("--------------fmtdesc--------------------------------------");
	struct v4l2_fmtdesc {         //VIDIOC_ENUM_FMT
		__u32		    index;             /* Format number      */
		__u32		    type;              /* enum v4l2_buf_type */
		__u32               flags;
		__u8		    description[32];   /* Description string */
		__u32		    pixelformat;       /* Format fourcc      */
		__u32		    mbus_code;		/* Media bus code    */
		__u32		    reserved[3];
	}fmtdesc;
	fmtdesc.index=0;    //从0输入index的值，开始查询，本机index=0,1
	fmtdesc.type=1;
	int t1=ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc);
	if(t1<0){
		puts("fmtdesc error");
	}
	printf("%s\n",fmtdesc.description);  //0：yuv422,1：mjpg
	fmtdesc.index=1;    //从0输入index的值，开始查询，本机index=0,1
	fmtdesc.type=1;
	int t2=ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc);
	if(t2<0){
		puts("fmtdesc error");
	}
	printf("%s\n",fmtdesc.description);  //0：yuv422,1：mjpg
	puts("-------------------frame_format--------------------------");
	
	struct v4l2_format {
		__u32	 type;
		union {
		//	struct v4l2_pix_format		pix;     /* V4L2_BUF_TYPE_VIDEO_CAPTURE */
			struct v4l2_pix_format {
				__u32			width;
				__u32			height;
				__u32			pixelformat;
				__u32			field;		/* enum v4l2_field */
				__u32			bytesperline;	/* for padding, zero if unused */
				__u32			sizeimage;
				__u32			colorspace;	/* enum v4l2_colorspace */
				__u32			priv;		/* private data, depends on pixelformat */
				__u32			flags;		/* format flags (V4L2_PIX_FMT_FLAG_*) */
				union {
					/* enum v4l2_ycbcr_encoding */
					__u32			ycbcr_enc;
					/* enum v4l2_hsv_encoding */
					__u32			hsv_enc;
				};
				__u32			quantization;	/* enum v4l2_quantization */
				__u32			xfer_func;	/* enum v4l2_xfer_func */
			}pix;
			struct v4l2_pix_format_mplane	pix_mp;  /* V4L2_BUF_TYPE_VIDEO_CAPTURE_MPLANE */
			struct v4l2_window		win;     /* V4L2_BUF_TYPE_VIDEO_OVERLAY */
			struct v4l2_vbi_format		vbi;     /* V4L2_BUF_TYPE_VBI_CAPTURE */
			struct v4l2_sliced_vbi_format	sliced;  /* V4L2_BUF_TYPE_SLICED_VBI_CAPTURE */
			struct v4l2_sdr_format		sdr;     /* V4L2_BUF_TYPE_SDR_CAPTURE */
			struct v4l2_meta_format		meta;    /* V4L2_BUF_TYPE_META_CAPTURE */
			__u8	raw_data[200];                   /* user-defined */
		} fmt;
	}format;
	format.type=1;
	int t3=ioctl(fd,VIDIOC_G_FMT,&format);
	if(t3<0){
		puts("format error");
	}
	printf("%d\n",format.fmt.pix.width);               //2560   支持最大宽度      
	printf("%d\n",format.fmt.pix.height);              //1440   支持图像的最高宽度
	printf("%x\n",format.fmt.pix.pixelformat);        //v4l2_fourcc值 47504a4d    4d=M 4a=J  50=P 47=G   16进制小序排列（反向）
 
	printf("%d\n",format.fmt.pix.field);              //1=V4L2_FIELD_NONE
	printf("%d\n",format.fmt.pix.sizeimage);          //7372800=2560*1440*16/8    每帧支持最大字节数
	puts("--------------------frame_size-------------------------------------");
	struct v4l2_frmsizeenum {
		__u32			index;		/* Frame size number */
		__u32			pixel_format;	/* Pixel format */
		__u32			type;		/* Frame size type the device supports. */
		
		union {					/* Frame size */
		  //	struct v4l2_frmsize_discrete	discrete;
			struct v4l2_frmsize_discrete {
				__u32			width;		/* Frame width [pixel] */
				__u32			height;		/* Frame height [pixel] */
			}discrete;
 
			struct v4l2_frmsize_stepwise	stepwise;
		};
		
		__u32   reserved[2];			/* Reserved space for future use */
	}frmsize;
    frmsize.index=0;
	frmsize.pixel_format=0x47504a4d;
	
	int t4=ioctl(fd,VIDIOC_ENUM_FRAMESIZES,&frmsize);
	if(t4<0){
		puts("frmsize error");
	}
	printf("%d\n",frmsize.discrete.width);
	return 0;
}