1、前言
在查看摄像头类型时，大致可以分为两类：Video Capture 和 Video Capture Multiplanar。
本次应用程序主要针对类型为Video Capture的相机。
2、环境介绍
rk3566 + uvc摄像头
3、步骤
应用程序编写主要分为以下几个步骤：
1、打开设备节点。
2、查询设备能力。
3、枚举支持的视频格式。
4、设置格式。
5、请求buffer。
6、buffer入队列。
7、打开相机。
8、buffer出队列。
9、保存图片。
10、buffer重新入队列。
11、关闭相机。
4、应用程序编写
完整的应用程序如下：
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <linux/types.h>
#include <linux/videodev2.h>
#include <poll.h>
#include <sys/mman.h>
#include <jpeglib.h>
#include <linux/fb.h>
#define FRAME_SIZE_X 640
#define FRAME_SIZE_Y 480
int main(int argc, char **argv)
{
int ret;
int fd;
struct v4l2_fmtdesc fmtdesc;
struct v4l2_frmsizeenum fsenum;
void *bufs[32];
int fmt_index = 0;
int frame_index = 0;
int buf_cnt;
int i;
int type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
struct pollfd fds[1];
char filename[32];
int file_cnt = 0;
if (argc != 2)
{
printf("Usage: %s </dev/videoX>\n", argv[0]);
return -1;
}
if (argv[1] == NULL)
goto _err;
/* 1. open /dev/video* */
fd = open(argv[1], O_RDWR);
if (fd < 0)
{
printf("can not open %s\n", argv[1]);
goto _err;
}
/* 2. query capability */
struct v4l2_capability cap;
memset(&cap, 0, sizeof(struct v4l2_capability));
if (0 == ioctl(fd, VIDIOC_QUERYCAP, &cap))
{
if ((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == 0)
{
fprintf(stderr, "Error opening device %s: video capture not supported.\n", argv[1]);
goto _ioc_querycap_err;
}
if(!(cap.capabilities & V4L2_CAP_STREAMING))
{
fprintf(stderr, "%s does not support streaming i/o\n", argv[1]);
goto _ioc_querycap_err;
}
}
else
{
printf("can not get capability\n");
goto _ioc_querycap_err;
}
/* 3. enum formt */
while (1)
{
fmtdesc.index = fmt_index;
fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if (0 != ioctl(fd, VIDIOC_ENUM_FMT, &fmtdesc))
break;
frame_index = 0;
printf("format %s,%d:\n", fmtdesc.description, fmtdesc.pixelformat);
while (1)
{
memset(&fsenum, 0, sizeof(struct v4l2_frmsizeenum));
fsenum.pixel_format = fmtdesc.pixelformat;
fsenum.index = frame_index;
/* get framesize */
if (ioctl(fd, VIDIOC_ENUM_FRAMESIZES, &fsenum) == 0)
{
printf("\t%d: %d x %d\n", frame_index, fsenum.discrete.width, fsenum.discrete.height);
}
else
{
break;
}
frame_index++;
}
fmt_index++;
}
/* 4. set formt */
struct v4l2_format fmt;
memset(&fmt, 0, sizeof(struct v4l2_format));
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
fmt.fmt.pix.width = FRAME_SIZE_X;
fmt.fmt.pix.height = FRAME_SIZE_Y;
fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
fmt.fmt.pix.field = V4L2_FIELD_ANY;
if (0 == ioctl(fd, VIDIOC_S_FMT, &fmt))
{
printf("the final frame-size has been set : %d x %d\n", fmt.fmt.pix.width, fmt.fmt.pix.height);
}
else
{
printf("can not set format\n");
goto _ioc_sfmt_err;
}
/* 5. require buffer */
struct v4l2_requestbuffers rb;
memset(&rb, 0, sizeof(struct v4l2_requestbuffers));
rb.count = 32;
rb.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
rb.memory = V4L2_MEMORY_MMAP;
if (0 == ioctl(fd, VIDIOC_REQBUFS, &rb))
{
buf_cnt = rb.count;
for(i = 0; i < rb.count; i++)
{
struct v4l2_buffer buf;
memset(&buf, 0, sizeof(struct v4l2_buffer));
buf.index = i;
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (0 == ioctl(fd, VIDIOC_QUERYBUF, &buf))
{
/* mmap */
bufs[i] = mmap(0, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);
if(bufs[i] == MAP_FAILED)
{
printf("Unable to map buffer");
goto _err;
}
}
else
{
printf("can not query buffer\n");
goto _err;
}
}
}
else
{
printf("can not request buffers\n");
goto _ioc_reqbufs_err;
}
/* 6. queue buffer */
for(i = 0; i < buf_cnt; ++i)
{
struct v4l2_buffer buf;
memset(&buf, 0, sizeof(struct v4l2_buffer));
buf.index = i;
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (0 != ioctl(fd, VIDIOC_QBUF, &buf))
{
perror("Unable to queue buffer");
goto _ioc_qbuf_err;
}
}
/* start camera */
if (0 != ioctl(fd, VIDIOC_STREAMON, &type))
{
printf("Unable to start capture\n");
goto _err;
}
printf("\nstart camera ...\n");
while (1)
{
/* poll */
memset(fds, 0, sizeof(fds));
fds[0].fd = fd;
fds[0].events = POLLIN;
if (1 == poll(fds, 1, -1))
{
/* dequeue buffer */
struct v4l2_buffer buf;
memset(&buf, 0, sizeof(struct v4l2_buffer));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
if (0 != ioctl(fd, VIDIOC_DQBUF, &buf))
{
printf("Unable to dequeue buffer\n");
goto _ioc_dqbuf_err;
}
/* save as .jpg */
sprintf(filename, "video_raw_data_%04d.jpg", file_cnt++);
int fd_file = open(filename, O_RDWR | O_CREAT, 0666);
if (fd_file < 0)
{
printf("can not create file : %s\n", filename);
}
printf("capture to %s\n", filename);
write(fd_file, bufs[buf.index], buf.bytesused);
close(fd_file);
/* queue buffer */
if (0 != ioctl(fd, VIDIOC_QBUF, &buf))
{
printf("Unable to queue buffer");
goto _ioc_qbuf_err;
}
}
}
/* close camera */
if (0 != ioctl(fd, VIDIOC_STREAMOFF, &type))
{
printf("Unable to stop capture\n");
goto _ioc_streamoff_err;
}
close(fd);
return 0;
_ioc_qbuf_err:
_ioc_reqbufs_err:
_ioc_sfmt_err:
_ioc_querycap_err:
_ioc_streamoff_err:
_ioc_dqbuf_err:
_err:
return -1;
}
5、测试
5.1、编译应用程序
如果你使用的buildroot系统，需要交叉编译。
这里测试所使用的板子跑的是ubuntu，执行如下命令直接编译：
sudo gcc -o uvc_to_jpg uvc_to_jpg.c
5.2、运行应用程序
sudo ./uvc_to_jpg /dev/video10
查看某一张jpg图片：
6、总结
源码gitee仓库：
仓库主页：
https://gitee.com/cattle_l/v4l2_app.git
直接拉取：
git clone https://gitee.com/cattle_l/v4l2_app.git