该方法只启动usb摄像头

import cv2

import numpy

import matplotlib.pyplot as plot

class Camera:

    cap = cv2.VideoCapture(0)

    @staticmethod

    def getCamera():

        ret, frame = Camera.cap.read()

        return ret, frame

    @staticmethod

    def getCap():

        return Camera.cap

def main():

    camera = Camera()

    while(1):

        ret, frame = camera.getCamera()

        cv2.imshow("capture", frame)

        if cv2.waitKey(1) & 0xFF == ord('q'):

            break

    camera.cap.release()

    # cv2.destroyAllWindows()

if __name__ == '__main__':

    main()

C++ start onboard camera

#include <stdio.h>

#include <opencv2/opencv.hpp>  

using namespace cv;

using namespace std;  

int main(int argc, char** argv)

{

    VideoCapture cap("nvcamerasrc ! video/x-raw(memory:NVMM), width=(int)1280, height=(int)720,format=(string)I420, framerate=(fraction)24/1 ! nvvidconv flip-method=2 ! video/x-raw, format=(string)BGRx ! videoconvert ! video/x-raw, format=(string)BGR ! appsink");

    if (!cap.isOpened())

    {

        cout << "Failed to open camera." << endl;

        return -;

    }  

    for(;;)

    {

        Mat frame;

        cap >> frame;

        imshow("original", frame);

        //waitKey(1);

        if(waitKey() >= )

        break;

    }

    return ;

}

C++ start usb camera

/*

Author:Jack-Cui

Blog:http://blog.csdn.net/c406495762

Time:25 May 2017

*/

#include <unistd.h>

#include <error.h>

#include <errno.h>

#include <fcntl.h>

#include <sys/ioctl.h>

#include <sys/types.h>

#include <pthread.h>

#include <linux/videodev2.h>

#include <sys/mman.h>

#include <opencv2/core/core.hpp>

#include <opencv2/highgui/highgui.hpp>

#include <stdio.h>

#include <stdlib.h>

#include <string.h>

#include <iostream>

#include <iomanip>

#include <string>

using namespace std;

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

#define IMAGEWIDTH 3264

#define IMAGEHEIGHT 2448

class V4L2Capture {

public:

    V4L2Capture(char *devName, int width, int height);

    virtual ~V4L2Capture();

    int openDevice();

    int closeDevice();

    int initDevice();

    int startCapture();

    int stopCapture();

    int freeBuffers();

    int getFrame(void **,size_t *);

    int backFrame();

    static void test();

private:

    int initBuffers();

    struct cam_buffer

    {

        void* start;

        unsigned int length;

    };

    char *devName;

    int capW;

    int capH;

    int fd_cam;

    cam_buffer *buffers;

    unsigned int n_buffers;

    int frameIndex;

};

V4L2Capture::V4L2Capture(char *devName, int width, int height) {

    // TODO Auto-generated constructor stub

    this->devName = devName;

    this->fd_cam = -;

    this->buffers = NULL;

    this->n_buffers = ;

    this->frameIndex = -;

    this->capW=width;

    this->capH=height;

}

V4L2Capture::~V4L2Capture() {

    // TODO Auto-generated destructor stub

}

int V4L2Capture::openDevice() {

    /*设备的打开*/

    printf("video dev : %s\n", devName);

    fd_cam = open(devName, O_RDWR);

    if (fd_cam < ) {

        perror("Can't open video device");

    }

    return ;

}

int V4L2Capture::closeDevice() {

    if (fd_cam > ) {

        int ret = ;

        if ((ret = close(fd_cam)) < ) {

            perror("Can't close video device");

        }

        return ;

    } else {

        return -;

    }

}

int V4L2Capture::initDevice() {

    int ret;

    struct v4l2_capability cam_cap;        //显示设备信息

    struct v4l2_cropcap cam_cropcap;    //设置摄像头的捕捉能力

    struct v4l2_fmtdesc cam_fmtdesc;    //查询所有支持的格式：VIDIOC_ENUM_FMT

    struct v4l2_crop cam_crop;            //图像的缩放

    struct v4l2_format cam_format;        //设置摄像头的视频制式、帧格式等

    /* 使用IOCTL命令VIDIOC_QUERYCAP，获取摄像头的基本信息*/

    ret = ioctl(fd_cam, VIDIOC_QUERYCAP, &cam_cap);

    if (ret < ) {

        perror("Can't get device information: VIDIOCGCAP");

    }

    printf(

            "Driver Name:%s\nCard Name:%s\nBus info:%s\nDriver Version:%u.%u.%u\n",

            cam_cap.driver, cam_cap.card, cam_cap.bus_info,

            (cam_cap.version >> ) & 0XFF, (cam_cap.version >> ) & 0XFF,

            cam_cap.version & 0XFF);

    /* 使用IOCTL命令VIDIOC_ENUM_FMT，获取摄像头所有支持的格式*/

    cam_fmtdesc.index = ;

    cam_fmtdesc.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    printf("Support format:\n");

    while (ioctl(fd_cam, VIDIOC_ENUM_FMT, &cam_fmtdesc) != -) {

        printf("\t%d.%s\n", cam_fmtdesc.index + , cam_fmtdesc.description);

        cam_fmtdesc.index++;

    }

    /* 使用IOCTL命令VIDIOC_CROPCAP，获取摄像头的捕捉能力*/

    cam_cropcap.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if ( == ioctl(fd_cam, VIDIOC_CROPCAP, &cam_cropcap)) {

        printf("Default rec:\n\tleft:%d\n\ttop:%d\n\twidth:%d\n\theight:%d\n",

                cam_cropcap.defrect.left, cam_cropcap.defrect.top,

                cam_cropcap.defrect.width, cam_cropcap.defrect.height);

        /* 使用IOCTL命令VIDIOC_S_CROP，获取摄像头的窗口取景参数*/

        cam_crop.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

        cam_crop.c = cam_cropcap.defrect;        //默认取景窗口大小

        if (- == ioctl(fd_cam, VIDIOC_S_CROP, &cam_crop)) {

            //printf("Can't set crop para\n");

        }

    } else {

        printf("Can't set cropcap para\n");

    }

    /* 使用IOCTL命令VIDIOC_S_FMT，设置摄像头帧信息*/

    cam_format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    cam_format.fmt.pix.width = capW;

    cam_format.fmt.pix.height = capH;

    cam_format.fmt.pix.pixelformat = V4L2_PIX_FMT_MJPEG;        //要和摄像头支持的类型对应

    cam_format.fmt.pix.field = V4L2_FIELD_INTERLACED;

    ret = ioctl(fd_cam, VIDIOC_S_FMT, &cam_format);

    if (ret < ) {

        perror("Can't set frame information");

    }

    /* 使用IOCTL命令VIDIOC_G_FMT，获取摄像头帧信息*/

    cam_format.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    ret = ioctl(fd_cam, VIDIOC_G_FMT, &cam_format);

    if (ret < ) {

        perror("Can't get frame information");

    }

    printf("Current data format information:\n\twidth:%d\n\theight:%d\n",

            cam_format.fmt.pix.width, cam_format.fmt.pix.height);

    ret = initBuffers();

    if (ret < ) {

        perror("Buffers init error");

        //exit(-1);

    }

    return ;

}

int V4L2Capture::initBuffers() {

    int ret;

    /* 使用IOCTL命令VIDIOC_REQBUFS，申请帧缓冲*/

    struct v4l2_requestbuffers req;

    CLEAR(req);

    req.count = ;

    req.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    req.memory = V4L2_MEMORY_MMAP;

    ret = ioctl(fd_cam, VIDIOC_REQBUFS, &req);

    if (ret < ) {

        perror("Request frame buffers failed");

    }

    if (req.count < ) {

        perror("Request frame buffers while insufficient buffer memory");

    }

    buffers = (struct cam_buffer*) calloc(req.count, sizeof(*buffers));

    if (!buffers) {

        perror("Out of memory");

    }

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

        struct v4l2_buffer buf;

        CLEAR(buf);

        // 查询序号为n_buffers 的缓冲区，得到其起始物理地址和大小

        buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

        buf.memory = V4L2_MEMORY_MMAP;

        buf.index = n_buffers;

        ret = ioctl(fd_cam, VIDIOC_QUERYBUF, &buf);

        if (ret < ) {

            printf("VIDIOC_QUERYBUF %d failed\n", n_buffers);

            return -;

        }

        buffers[n_buffers].length = buf.length;

        //printf("buf.length= %d\n",buf.length);

        // 映射内存

        buffers[n_buffers].start = mmap(

                NULL, // start anywhere

                buf.length, PROT_READ | PROT_WRITE, MAP_SHARED, fd_cam,

                buf.m.offset);

        if (MAP_FAILED == buffers[n_buffers].start) {

            printf("mmap buffer%d failed\n", n_buffers);

            return -;

        }

    }

    return ;

}

int V4L2Capture::startCapture() {

    unsigned int i;

    for (i = ; 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 (- == ioctl(fd_cam, VIDIOC_QBUF, &buf)) {

            printf("VIDIOC_QBUF buffer%d failed\n", i);

            return -;

        }

    }

    enum v4l2_buf_type type;

    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (- == ioctl(fd_cam, VIDIOC_STREAMON, &type)) {

        printf("VIDIOC_STREAMON error");

        return -;

    }

    return ;

}

int V4L2Capture::stopCapture() {

    enum v4l2_buf_type type;

    type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    if (- == ioctl(fd_cam, VIDIOC_STREAMOFF, &type)) {

        printf("VIDIOC_STREAMOFF error\n");

        return -;

    }

    return ;

}

int V4L2Capture::freeBuffers() {

    unsigned int i;

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

        if (- == munmap(buffers[i].start, buffers[i].length)) {

            printf("munmap buffer%d failed\n", i);

            return -;

        }

    }

    free(buffers);

    return ;

}

int V4L2Capture::getFrame(void **frame_buf, size_t* len) {

    struct v4l2_buffer queue_buf;

    CLEAR(queue_buf);

    queue_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

    queue_buf.memory = V4L2_MEMORY_MMAP;

    if (- == ioctl(fd_cam, VIDIOC_DQBUF, &queue_buf)) {

        printf("VIDIOC_DQBUF error\n");

        return -;

    }

    *frame_buf = buffers[queue_buf.index].start;

    *len = buffers[queue_buf.index].length;

    frameIndex = queue_buf.index;

    return ;

}

int V4L2Capture::backFrame() {

    if (frameIndex != -) {

        struct v4l2_buffer queue_buf;

        CLEAR(queue_buf);

        queue_buf.type = V4L2_BUF_TYPE_VIDEO_CAPTURE;

        queue_buf.memory = V4L2_MEMORY_MMAP;

        queue_buf.index = frameIndex;

        if (- == ioctl(fd_cam, VIDIOC_QBUF, &queue_buf)) {

            printf("VIDIOC_QBUF error\n");

            return -;

        }

        return ;

    }

    return -;

}

void V4L2Capture::test() {

    unsigned char *yuv422frame = NULL;

    unsigned long yuvframeSize = ;

    string videoDev="/dev/video0";

    V4L2Capture *vcap = new V4L2Capture(const_cast<char*>(videoDev.c_str()),

            , );

    vcap->openDevice();

    vcap->initDevice();

    vcap->startCapture();

    vcap->getFrame((void **) &yuv422frame, (size_t *)&yuvframeSize);

    vcap->backFrame();

    vcap->freeBuffers();

    vcap->closeDevice();

}

void VideoPlayer() {

    unsigned char *yuv422frame = NULL;

    unsigned long yuvframeSize = ;

    string videoDev = "/dev/video0";

    V4L2Capture *vcap = new V4L2Capture(const_cast<char*>(videoDev.c_str()), , );

    vcap->openDevice();

    vcap->initDevice();

    vcap->startCapture();

    cvNamedWindow("Capture",CV_WINDOW_AUTOSIZE);

    IplImage* img;

    CvMat cvmat;

    double t;

    while(){

        t = (double)cvGetTickCount();

        vcap->getFrame((void **) &yuv422frame, (size_t *)&yuvframeSize);

        cvmat = cvMat(IMAGEHEIGHT,IMAGEWIDTH,CV_8UC3,(void*)yuv422frame);        //CV_8UC3

        //解码

        img = cvDecodeImage(&cvmat,);

        if(!img){

            printf("DecodeImage error!\n");

        }

        cvShowImage("Capture",img);

        cvReleaseImage(&img);

        vcap->backFrame();

        if((cvWaitKey()&) == ){

            exit();

        }

        t = (double)cvGetTickCount() - t;

        printf("Used time is %g ms\n",( t / (cvGetTickFrequency()*)));

    }

    vcap->stopCapture();

    vcap->freeBuffers();

    vcap->closeDevice();

}

int main() {

    VideoPlayer();

    return ;

}

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