linux下摄像头图像数据的获取

2.6.32内核，V4L2架构

亲自测试可用

在友善之臂MINI2440开发板上测试可用

源程序如下

 

#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 CLEAR(x) memset (&(x), 0, sizeof (x))



struct buffer {

        void *                  start;

        size_t                  length;

};



static char *           dev_name        = "/dev/video0";//摄像头设备名

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;

//////////////////////////////////////////////////////

//获取一帧数据

//////////////////////////////////////////////////////

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"); //出列采集的帧缓冲



	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); //将其写入文件中

  

	ff=ioctl (fd, VIDIOC_QBUF, &buf); //再将其入列

	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.jpg", "wb");                 //图片文件名



	fd = open (dev_name, O_RDWR /* required */ |O_NONBLOCK);//打开设备

	if(fd<0)

	{	

		perror("open faiure!");

		exit(1);

	}

	int ff=ioctl (fd, VIDIOC_QUERYCAP, &cap);               //获取摄像头参数

	if(ff<0)

		printf("failture VIDIOC_QUERYCAP\n");



	struct v4l2_fmtdesc fmt1;

    int ret;

	memset(&fmt1, 0, sizeof(fmt1));

	fmt1.index = 0;            //初始化为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.width       = 320; 

	fmt.fmt.pix.height      = 240;

	fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_JPEG;//V4L2_PIX_FMT_YUYV;//V4L2_PIX_FMT_YVU420;//V4L2_PIX_FMT_YUYV;

	fmt.fmt.pix.field       = V4L2_FIELD_INTERLACED;

	ff = ioctl (fd, VIDIOC_S_FMT, &fmt); //设置图像格式

	if(ff<0)

		printf("failture VIDIOC_S_FMT\n");

	file_length = fmt.fmt.pix.bytesperline * fmt.fmt.pix.height; //计算图片大小



	struct v4l2_requestbuffers req;

	CLEAR (req);

	req.count               = 1;

	req.type                = V4L2_BUF_TYPE_VIDEO_CAPTURE;

	req.memory              = V4L2_MEMORY_MMAP;



	ff=ioctl (fd, VIDIOC_REQBUFS, &req); //申请缓冲，count是申请的数量

	if(ff<0)

		printf("failture VIDIOC_REQBUFS\n");

	if (req.count < 1)

		printf("Insufficient buffer memory\n");



	buffers = calloc (req.count, sizeof (*buffers));//内存中建立对应空间



	for (n_buffers = 0; n_buffers < req.count; ++n_buffers) 

	{

		struct v4l2_buffer buf;   //驱动中的一帧

		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)) //映射用户空间

			printf ("VIDIOC_QUERYBUF error\n");



		buffers[n_buffers].length = buf.length;

		buffers[n_buffers].start =

		mmap (NULL /* start anywhere */,    //通过mmap建立映射关系

			buf.length,

			PROT_READ | PROT_WRITE /* required */,

			MAP_SHARED /* recommended */,

			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))//申请到的缓冲进入列队

			printf ("VIDIOC_QBUF failed\n");

	}

                

	type = V4L2_BUF_TYPE_VIDEO_CAPTURE;



	if (-1 == ioctl (fd, VIDIOC_STREAMON, &type)) //开始捕捉图像数据

		printf ("VIDIOC_STREAMON failed\n");



	for (;;) //这一段涉及到异步IO

	{

		fd_set fds;

		struct timeval tv;

		int r;



		FD_ZERO (&fds);//将指定的文件描述符集清空

		FD_SET (fd, &fds);//在文件描述符集合中增加一个新的文件描述符



	   /* Timeout. */

		tv.tv_sec = 2;

		tv.tv_usec = 0;



		r = select (fd + 1, &fds, NULL, NULL, &tv);//判断是否可读（即摄像头是否准备好），tv是定时



		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 ())//如果可读，执行read_frame ()函数，并跳出循环

			break;

	}



unmap:

	for (i = 0; i < n_buffers; ++i)

		if (-1 == munmap (buffers[i].start, buffers[i].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);

return 0;

}

 

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