V4L2应用层编程
#include <stdio.h>
#include <string.h>
#include <errno.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/mman.h>
#include <assert.h>
#include <linux/videodev2.h>
typedef struct
{
void *start;
int length;
}BUFTYPE;
BUFTYPE *user_buf;
int n_buffer = 0;
//打开摄像头设备
int open_camer_device()
{
int fd;
if((fd = open("/dev/video0",O_RDWR | O_NONBLOCK)) < 0)
{
perror("Fail to open");
exit(EXIT_FAILURE);
}
return fd;
}
int init_mmap(int fd)
{
int i = 0;
struct v4l2_requestbuffers reqbuf;
bzero(&reqbuf,sizeof(reqbuf));
reqbuf.count = 4;
reqbuf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
reqbuf.memory = V4L2_MEMORY_MMAP;
//申请视频缓冲区(这个缓冲区位于内核空间，需要通过mmap映射)
//这一步操作可能会修改reqbuf.count的值，修改为实际成功申请缓冲区个数
if(-1 == ioctl(fd,VIDIOC_REQBUFS,&reqbuf))
{
perror("Fail to ioctl 'VIDIOC_REQBUFS'");
exit(EXIT_FAILURE);
}
n_buffer = reqbuf.count;
printf("n_buffer = %d\n",n_buffer);
user_buf = calloc(reqbuf.count,sizeof(*user_buf));
if(user_buf == NULL){
fprintf(stderr,"Out of memory\n");
exit(EXIT_FAILURE);
}
//将内核缓冲区映射到用户进程空间
for(i = 0; i < reqbuf.count; i ++)
{
struct v4l2_buffer buf;
bzero(&buf,sizeof(buf));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
//查询申请到内核缓冲区的信息
if(-1 == ioctl(fd,VIDIOC_QUERYBUF,&buf))
{
perror("Fail to ioctl : VIDIOC_QUERYBUF");
exit(EXIT_FAILURE);
}
user_buf[i].length = buf.length;
user_buf[i].start =
mmap(
NULL,/*start anywhere*/
buf.length,
PROT_READ | PROT_WRITE,
MAP_SHARED,
fd,buf.m.offset
);
if(MAP_FAILED == user_buf[i].start)
{
perror("Fail to mmap");
exit(EXIT_FAILURE);
}
}
return 0;
}
//初始化视频设备
int init_camer_device(int fd)
{
struct v4l2_fmtdesc fmt;
struct v4l2_capability cap;
struct v4l2_format stream_fmt;
int ret;
//当前视频设备支持的视频格式
memset(&fmt,0,sizeof(fmt));
fmt.index = 0;
fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
while((ret = ioctl(fd,VIDIOC_ENUM_FMT,&fmt)) == 0)
{
fmt.index ++ ;
printf("{pixelformat = %c%c%c%c},description = '%s'\n",
fmt.pixelformat & 0xff,(fmt.pixelformat >> 8)&0xff,
(fmt.pixelformat >> 16) & 0xff,(fmt.pixelformat >> 24)&0xff,
fmt.description);
}
//查询视频设备驱动的功能
ret = ioctl(fd,VIDIOC_QUERYCAP,&cap);
if(ret < 0){
perror("FAIL to ioctl VIDIOC_QUERYCAP");
exit(EXIT_FAILURE);
}
//判断是否是一个视频捕捉设备
if(!(cap.capabilities & V4L2_BUF_TYPE_VIDEO_CAPTURE))
{
printf("The Current device is not a video capture device\n");
exit(EXIT_FAILURE);
}
//判断是否支持视频流形式
if(!(cap.capabilities & V4L2_CAP_STREAMING))
{
printf("The Current device does not support streaming i/o\n");
exit(EXIT_FAILURE);
}
//设置摄像头采集数据格式，如设置采集数据的
//长,宽，图像格式(JPEG,YUYV,MJPEG等格式)
stream_fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
stream_fmt.fmt.pix.width = 680;
stream_fmt.fmt.pix.height = 480;
stream_fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;
stream_fmt.fmt.pix.field = V4L2_FIELD_INTERLACED;
if(-1 == ioctl(fd,VIDIOC_S_FMT,&stream_fmt))
{
perror("Fail to ioctl");
exit(EXIT_FAILURE);
}
//初始化视频采集方式(mmap)
init_mmap(fd);
return 0;
}
int start_capturing(int fd)
{
unsigned int i;
enum v4l2_buf_type type;
//将申请的内核缓冲区放入一个队列中
for(i = 0;i < n_buffer;i ++)
{
struct v4l2_buffer buf;
bzero(&buf,sizeof(buf));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
buf.index = i;
if(-1 == ioctl(fd,VIDIOC_QBUF,&buf))
{
perror("Fail to ioctl 'VIDIOC_QBUF'");
exit(EXIT_FAILURE);
}
}
//开始采集数据
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if(-1 == ioctl(fd,VIDIOC_STREAMON,&type))
{
printf("i = %d.\n",i);
perror("Fail to ioctl 'VIDIOC_STREAMON'");
exit(EXIT_FAILURE);
}
return 0;
}
//将采集好的数据放到文件中
int process_image(void *addr,int length)
{
FILE *fp;
static int num = 0;
char picture_name[20];
sprintf(picture_name,"picture%d.jpg",num ++);
if((fp = fopen(picture_name,"w")) == NULL)
{
perror("Fail to fopen");
exit(EXIT_FAILURE);
}
fwrite(addr,length,1,fp);
usleep(500);
fclose(fp);
return 0;
}
int read_frame(int fd)
{
struct v4l2_buffer buf;
unsigned int i;
bzero(&buf,sizeof(buf));
buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
buf.memory = V4L2_MEMORY_MMAP;
//从队列中取缓冲区
if(-1 == ioctl(fd,VIDIOC_DQBUF,&buf))
{
perror("Fail to ioctl 'VIDIOC_DQBUF'");
exit(EXIT_FAILURE);
}
assert(buf.index < n_buffer);
//读取进程空间的数据到一个文件中
process_image(user_buf[buf.index].start,user_buf[buf.index].length);
if(-1 == ioctl(fd,VIDIOC_QBUF,&buf))
{
perror("Fail to ioctl 'VIDIOC_QBUF'");
exit(EXIT_FAILURE);
}
return 1;
}
int mainloop(int fd)
{
int count = 10;
while(count -- > 0)
{
for(;;)
{
fd_set fds;
struct timeval tv;
int r;
FD_ZERO(&fds);
FD_SET(fd,&fds);
/*Timeout*/
tv.tv_sec = 2;
tv.tv_usec = 0;
r = select(fd + 1,&fds,NULL,NULL,&tv);
if(-1 == r)
{
if(EINTR == errno)
continue;
perror("Fail to select");
exit(EXIT_FAILURE);
}
if(0 == r)
{
fprintf(stderr,"select Timeout\n");
exit(EXIT_FAILURE);
}
if(read_frame(fd))
break;
}
}
return 0;
}
void stop_capturing(int fd)
{
enum v4l2_buf_type type;
type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
if(-1 == ioctl(fd,VIDIOC_STREAMOFF,&type))
{
perror("Fail to ioctl 'VIDIOC_STREAMOFF'");
exit(EXIT_FAILURE);
}
return;
}
void uninit_camer_device()
{
unsigned int i;
for(i = 0;i < n_buffer;i ++)
{
if(-1 == munmap(user_buf[i].start,user_buf[i].length))
{
exit(EXIT_FAILURE);
}
}
free(user_buf);
return;
}
void close_camer_device(int fd)
{
if(-1 == close(fd))
{
perror("Fail to close fd");
exit(EXIT_FAILURE);
}
return;
}
int main()
{
int fd;
fd = open_camer_device();
init_camer_device(fd);
start_capturing(fd);
mainloop(fd);
stop_capturing(fd);
uninit_camer_device(fd);
close_camer_device(fd);
return 0;
}
注意：每个摄像头采集出来的数据格式可能不一样，一般支持MJPEG,JPEG格式的摄像头，采集出来的数据可以直接放在文件中，然后用图片查看器显示。
注意：每个摄像头采集出来的数据格式可能不一样，一般支持MJPEG,JPEG格式的摄像头，采集出来的数据可以直接放在文件中，然后用图片查看器显示。