V4L2采集图像基本流程

参考 http://blog.csdn.net/tsuibeyond/article/details/50654823

         http://www.cnblogs.com/surpassal/archive/2012/12/19/zed_webcam_lab1.html

      1.打开设备fd = open(FILE_VIDEO1, O_RDWR))

       2.取得设备的capability 看看设备具有什么功能 比如是否具有视频输入 或者音频输入输出等 VIDIOC QUERYCAP struct v4l2 capabilit

      3 选择视频输入 一个视频设备可以有多个视频输入 VIDIOC S INPUT struct v4l2 input

      4 设置视频的制式和帧格式 制式包括PAL NTSC 帧的格式个包括宽度和高度等 VIDIOC S STD VIDIOC S FMT struct v4l2 std id struct v4l2 format 

      5 向驱动申请帧缓冲 一般不超过5个 struct v4l2 requestbuffers 

      6 将申请到的帧缓冲映射到用户空间 这样就可以直接操作采集到的帧了 而不必去复制 mmap 

      7 将申请到的帧缓冲全部入队列 以便存放采集到的数据 VIDIOC QBUF struct v4l2 buffer 

      8 开始视频的采集 VIDIOC STREAMON

      9 出队列以取得已采集数据的帧缓冲 取得原始采集数据 VIDIOC DQBUF 

      10 将缓冲重新入队列尾 这样可以循环采集 VIDIOC QBUF 

     11 停止视频的采集 VIDIOC STREAMOFF 12 关闭视频设备 close fd ;

  

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include

uchar *buffer;                          //buffers 指针记录缓冲帧

#define IMAGEWIDTH 640
#define IMAGEHEIGHT 480

#define TRUE 1
#define FALSE 0

#define FILE_VIDEO1 "/dev/video0"

static int fd;                          //设备描述符
struct v4l2_streamparm setfps;          //结构体v4l2_streamparm来描述视频流的属性
struct v4l2_capability cap;             //取得设备的capability，看看设备具有什么功能，比如是否具有视频输入,或者音频输入输出等
struct v4l2_fmtdesc fmtdesc;            //枚举设备所支持的image format:  VIDIOC_ENUM_FMT
struct v4l2_format fmt,fmtack;          //子结构体struct v4l2_pix_format设置摄像头采集视频的宽高和类型：V4L2_PIX_FMT_YYUV V4L2_PIX_FMT_YUYV
struct v4l2_requestbuffers req;         //向驱动申请帧缓冲的请求，里面包含申请的个数
struct v4l2_buffer buf;                 //代表驱动中的一帧
enum   v4l2_buf_type type;              //帧类型

int init_v4l2(void);                    //初始化
int v4l2_grab(void);                    //采集



int main()
{
        printf("first~~\n");
        if(init_v4l2() == FALSE){      //打开摄像头
            printf("Init fail~~\n");
            exit(1);
        }
        printf("second~~\n");
        if(v4l2_grab() == FALSE){
            printf("grab fail~~\n");
            exit(2);
        }
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;           //Stream 或者Buffer的类型。此处肯定为V4L2_BUF_TYPE_VIDEO_CAPTURE
        buf.memory = V4L2_MEMORY_MMAP;                    //既然是Memory Mapping模式，则此处设置为：V4L2_MEMORY_MMAP
        printf("third~~\n");
        cvNamedWindow("one",CV_WINDOW_AUTOSIZE);
        IplImage* img;
        CvMat cvmat;
        int i = 100;
        double t;
        while(1){
                t = (double)cvGetTickCount();                      //调用时钟测时间
                ioctl(fd,VIDIOC_DQBUF,&buf);
                buf.index = 0;
                cvmat = cvMat(IMAGEHEIGHT,IMAGEWIDTH,CV_8UC3,(void*)buffer);//CV_8UC3
                //t = (double)cvGetTickCount();
                img = cvDecodeImage(&cvmat,1);
                //t=(double)cvGetTickCount()-t;
                //printf("used time is %gms\n",(t/(cvGetTickFrequency()*1000)));
                if(!img)    printf("No img\n");
                cvShowImage("one",img);
                cvReleaseImage(&img);
                ioctl(fd,VIDIOC_QBUF,&buf);                      //在 driver 内部管理着两个 buffer queues ，一个输入队列，一个输出队列。
                                                 //对于 capture device 来说，当输入队列中的 buffer 被塞满数据以后会自动变为输出队列，
                                                 //等待调用 VIDIOC_DQBUF 将数据进行处理以后重新调用 VIDIOC_QBUF 将 buffer 重新放进输入队列.
                if((cvWaitKey(1)&255) == 27)    exit(0);
                t=(double)cvGetTickCount()-t;
                printf("used time is %gms\n",(t/(cvGetTickFrequency()*1000)));
        }

        ioctl(fd,VIDIOC_STREAMOFF,&type);         // 停止视频采集命令，应用程序调用VIDIOC_ STREAMOFF停止视频采集命令后，视频设备驱动程序不在采集视频数据。
        return 0;
}

int init_v4l2(void){
        if ((fd = open(FILE_VIDEO1, O_RDWR)) == -1){
            printf("Opening video device error\n");
            return FALSE;
        }
        if (ioctl(fd, VIDIOC_QUERYCAP, &cap) == -1){               // 查询视频设备的功能
                printf("unable Querying Capabilities\n");
                return FALSE;
        }
        else
/*
        {
        printf( "Driver Caps:\n"
                "  Driver: \"%s\"\n"
                "  Card: \"%s\"\n"
                "  Bus: \"%s\"\n"
                "  Version: %d\n"
                "  Capabilities: %x\n",
                cap.driver,
                cap.card,
                cap.bus_info,
                cap.version,
                cap.capabilities);

        }

        if((cap.capabilities & V4L2_CAP_VIDEO_CAPTURE) == V4L2_CAP_VIDEO_CAPTURE){
            printf("Camera device %s: support capture\n",FILE_VIDEO1);
        }
        if((cap.capabilities & V4L2_CAP_STREAMING) == V4L2_CAP_STREAMING){
            printf("Camera device %s: support streaming.\n",FILE_VIDEO1);
        }
*/
        fmtdesc.index = 0;
        fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        printf("Support format: \n");
        while(ioctl(fd,VIDIOC_ENUM_FMT,&fmtdesc) != -1){        // 获取当前视频设备支持的视频格式
            printf("\t%d. %s\n",fmtdesc.index+1,fmtdesc.description);
            fmtdesc.index++;
        }
        //set fmt
        fmt.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        fmt.fmt.pix.width = IMAGEWIDTH;
        fmt.fmt.pix.height = IMAGEHEIGHT;
        fmt.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG; //*************************V4L2_PIX_FMT_YUYV****************可以选择
        fmt.fmt.pix.field = V4L2_FIELD_NONE;

        if (ioctl(fd, VIDIOC_S_FMT, &fmt) == -1){    // 设置视频设备的视频数据格式，例如设置视频图像数据的长、宽，图像格式（JPEG、YUYV格式）
            printf("Setting Pixel Format error\n");
            return FALSE;
        }
        if(ioctl(fd,VIDIOC_G_FMT,&fmt) == -1){   //获取图像格式
            printf("Unable to get format\n");
            return FALSE;
        }
//        else

/*        {
            printf("fmt.type:\t%d\n",fmt.type);         //可以输出图像的格式
            printf("pix.pixelformat:\t%c%c%c%c\n",fmt.fmt.pix.pixelformat & 0xFF,(fmt.fmt.pix.pixelformat >> 8) & 0xFF,\
                   (fmt.fmt.pix.pixelformat >> 16) & 0xFF, (fmt.fmt.pix.pixelformat >> 24) & 0xFF);
            printf("pix.height:\t%d\n",fmt.fmt.pix.height);
            printf("pix.field:\t%d\n",fmt.fmt.pix.field);
        }
*/
/*
        setfps.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        setfps.parm.capture.timeperframe.numerator = 100;
        setfps.parm.capture.timeperframe.denominator = 100;
        printf("init %s is OK\n",FILE_VIDEO1);
*/
        return TRUE;
}

int v4l2_grab(void){
    //struct v4l2_requestbuffers req = {0};
    //4  request for 4 buffers
    req.count = 1;
    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    req.memory = V4L2_MEMORY_MMAP;

    if (ioctl(fd, VIDIOC_REQBUFS, &req) == -1)        //开启内存映射或用户指针I/O
    {
        printf("Requesting Buffer error\n");
        return FALSE;
    }
    //5 mmap for buffers
    buffer = (uchar*)malloc(req.count * sizeof(*buffer));
    if(!buffer){
        printf("Out of memory\n");
        return FALSE;
    }
    unsigned int n_buffers;
    for(n_buffers = 0;n_buffers < req.count; n_buffers++){
    //struct v4l2_buffer buf = {0};
    buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    buf.memory = V4L2_MEMORY_MMAP;
    buf.index = n_buffers;
    if(ioctl(fd, VIDIOC_QUERYBUF, &buf) == -1){ // 查询已经分配的V4L2的视频缓冲区的相关信息，包括视频缓冲区的使用状态、在内核空间的偏移地址、缓冲区长度等。
        printf("Querying Buffer error\n");
        return FALSE;
        }

    buffer = (uchar*)mmap (NULL, buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd, buf.m.offset);

    if(buffer == MAP_FAILED){
        printf("buffer map error\n");
        return FALSE;
        }
    printf("Length: %d\nAddress: %p\n", buf.length, buffer);
    printf("Image Length: %d\n", buf.bytesused);
    }
    //6 queue
    for(n_buffers = 0;n_buffers
        buf.index = n_buffers;
        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
        buf.memory = V4L2_MEMORY_MMAP;
        if(ioctl(fd,VIDIOC_QBUF,&buf)){    // 投放一个空的视频缓冲区到视频缓冲区输入队列中
            printf("query buffer error\n");
            return FALSE;
        }
    }
    //7 starting
    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;
    if(ioctl(fd,VIDIOC_STREAMON,&type) == -1){ //
        printf("stream on error\n");
        return FALSE;
    }
    return TRUE;
}

可以设置采集图像的大小类型。

http://download.csdn.net/detail/yuyangyg/9780338  这里面有V4L2的一些资料