目前在人脸识别领域中，网络摄像头的使用很普遍，但接入网络摄像头和人脸识别SDK有一定门槛，在此文章中有介绍过虹软人脸识别SDK的接入流程，本文着重介绍网络摄像头获取视频流并处理的流程(红色框内)，以下内容仅供参考。
![门禁系统](http://img.blog.itpub.net/blog/2019/12/23/da70d552906ea12d.png?x-oss-process=style/bb "门禁系统")
## 1.海康SDK接入基本流程
**a.初始化并登录验证**
```cpp
        NET_DVR_Init();
        NET_DVR_DEVICEINFO_V30 struDeviceInfo = { 0 };
        long lUserID = NET_DVR_Login_V30(m_cameraIp, m_cameraPort,
            m_cameraUser, m_cameraPwd, &struDeviceInfo);
        if (lUserID < 0)
        {
            NET_DVR_Cleanup();
            return false;
        }

```
**b.创建线程并注册回调函数**
```cpp
        thread videoThread(&HCNetCamera::getCameraPreview, this);
        videoThread.detach();
        
        bool HCNetCamera::getCameraPreview()
        {
            NET_DVR_CLIENTINFO ClientInfo;
            ClientInfo.lChannel = 1; //Channel number 设备通道号
            ClientInfo.hPlayWnd = NULL;  //窗口为空，设备SDK不解码只取流
            ClientInfo.lLinkMode = 0;    //Main Stream
            ClientInfo.sMultiCastIP = NULL;
            //预览取流 
            g_realHandle = NET_DVR_RealPlay_V30(g_cameraUserId, &ClientInfo, fRealDataCallBack, NULL, TRUE);
            if (g_realHandle < 0)
            {
                qDebug() << "NET_DVR_RealPlay_V30 failed! Error number: " << NET_DVR_GetLastError();
                return false;
            }
            return true;
        }

```
**c.使用回调接口，获取实时的视频帧数据**
```cpp
        void CALLBACK fRealDataCallBack(LONG lRealHandle, DWORD dwDataType, BYTE *pBuffer, DWORD dwBufSize, void *pUser)
        {
            UNREFERENCED_PARAMETER(lRealHandle);
            UNREFERENCED_PARAMETER(pUser);

DWORD dRet = 0;
            BOOL inData = FALSE;

switch (dwDataType)
            {
            case NET_DVR_SYSHEAD:
                if (g_cameraPort >= 0)
                {
                    break; //同一路码流不需要多次调用开流接口
                }
                if (!PlayM4_GetPort(&g_cameraPort))
                {
                    break;
                }
                if (!PlayM4_OpenStream(g_cameraPort, pBuffer, dwBufSize, 1024 * 1024))
                {
                    dRet = PlayM4_GetLastError(g_cameraPort);
                    break;
                }
                //设置解码回调函数 
                if (!PlayM4_SetDecCallBack(g_cameraPort, DecCBFun))
                {
                    dRet = PlayM4_GetLastError(g_cameraPort);
                    break;
                }
                //打开视频解码
                if (!PlayM4_Play(g_cameraPort, NULL))
                {
                    dRet = PlayM4_GetLastError(g_cameraPort);
                    break;
                }
                dRet = PlayM4_GetLastError(g_cameraPort);
                break;

case NET_DVR_STREAMDATA:       //视频流数据
            default:
                inData = PlayM4_InputData(g_cameraPort, pBuffer, dwBufSize);
                while (!inData)
                {
                    Sleep(10);
                    inData = PlayM4_InputData(g_cameraPort, pBuffer, dwBufSize);
                    dRet = PlayM4_GetLastError(g_cameraPort);
                    OutputDebugString(L"PlayM4_InputData failed \n");
                }
                break;
            }
        }
```
```cpp
        //解码回调 视频为YUV数据(YV12)
        void CALLBACK DecCBFun(long port, char * pBuf, long nSize, FRAME_INFO * pFrameInfo, long nReserved1, long nReserved2)
        {
            UNREFERENCED_PARAMETER(nReserved1);
            UNREFERENCED_PARAMETER(nReserved2);
            UNREFERENCED_PARAMETER(nSize);
            UNREFERENCED_PARAMETER(port);

//图像格式转换 
            if (pFrameInfo->nType == T_YV12)
            {
                {
                    lock_guard<mutex> locker(g_CameraMutex);

Utils_ns::ImageUtils_ns::YV12ToBGR24_FFMPEG((unsigned char*)pBuf, (unsigned char*)g_curRGBImage->imageData,
                        pFrameInfo->nWidth, pFrameInfo->nHeight);//得到全部RGB图像 
                }
            }
        }
```
**d.应用层获取视频帧，这里为了简化操作，只获取了当前帧；大家也可以使用线程安全队列来处理**
```cpp
        int HCNetCamera::getFrame(Mat& image)
        {
            lock_guard<mutex> locker(g_CameraMutex);
            if (g_curRGBImage && g_curRGBImage->imageData)
            {
                image = g_curRGBImage;
                return 0;
            }
            return -1;
        }
        
        //以下是线程函数的一部分，主要是取帧，然后进行人脸检测
        {
            lock_guard<std::mutex> locker(g_CameraMutex);
            int ret = m_camera->getFrame(curFrame);
            if (ret == -1)
            {
                continue;
            }
        }
        
        ftProcessor->faceDetect(curFrame);
```
## 2.基本图像格式转换
目前虹软SDK支持以下几种图像数据格式：
![虹软SDK说明文档](http://img.blog.itpub.net/blog/2019/12/23/59f97455ddf8ebf4.png?x-oss-process=style/bb "虹软SDK说明文档")
在实际开发过程中一般使用opencv，opencv默认的图像数据格式是BGR24，而我使用的海康摄像头视频编码格式是H264，视频帧数据格式是YV12，因此需要将YV12转换为BGR24 ，同时也会说明下怎么转换为虹软SDK支持的其它格式，主要参考了[2]，以下的代码仅供参考。

**a.YV12 To BGR24**
```cpp
void yv12ToBGR24(unsigned char* yv12, unsigned  char* bgr24, int width, int height)
{
    unsigned char* y_yv12 = yv12;
    unsigned char* v_yv12 = yv12 + width*height;
    unsigned char* u_yv12 = yv12 + width*height + width*height / 4;

unsigned char* b = bgr24;
    unsigned char* g = bgr24 + 1;
    unsigned char* r = bgr24 + 2;

int yIndex, uIndex, vIndex;
    for (int i = 0; i < height; ++i)
    {
        for (int j = 0; j < width; ++j)
        {
            yIndex = i * width + j;
            vIndex = (i / 2) * (width / 2) + (j / 2);
            uIndex = vIndex;

*b = (unsigned char)(y_yv12[yIndex] + 1.732446 * (u_yv12[vIndex] - 128));
            *g = (unsigned char)(y_yv12[yIndex] - 0.698001 * (u_yv12[uIndex] - 128) - 0.703125 * (v_yv12[vIndex] - 128));
            *r = (unsigned char)(y_yv12[yIndex] + 1.370705 * (v_yv12[uIndex] - 128));

b += 3;
            g += 3;
            r += 3;
        }
    }
}

```
**b.YV12 To I420**
```cpp
void yv12ToI420(unsigned char* yv12, unsigned char* i420, int width, int height)
{
    unsigned char* y_yv12 = yv12;
    unsigned char* v_yv12 = yv12 + width*height;
    unsigned char* u_yv12 = yv12 + width*height + width*height / 4;

unsigned char* y_i420 = i420;
    unsigned char* u_i420 = i420 + width*height;
    unsigned char* v_i420 = i420 + width*height + width*height / 4;

memcpy(i420, yv12, width*height);
    memcpy(v_i420, v_yv12, width*height / 4);
    memcpy(u_i420, u_yv12, width*height / 4);

}
```
**c.YV12 To NV21**
```cpp
void yv12ToNV21(unsigned char* yv12, unsigned char* nv21, int width, int height)
{
    unsigned char* y_yv12 = yv12;
    unsigned char* v_yv12 = yv12 + width*height;
    unsigned char* u_yv12 = yv12 + width*height + width*height / 4;

unsigned char* y_nv21 = nv21;
    unsigned char* v_nv21 = nv21 + width*height;
    unsigned char* u_nv21 = nv21 + width*height + 1;

memcpy(nv21, yv12, width*height);

for (int i = 0; i < width*height / 4; ++i)
    {
        *v_nv21 = *v_yv12;
        *u_nv21 = *u_yv12;

v_nv21 += 2;
        u_nv21 += 2;

++v_yv12;
        ++u_yv12;
    }
}

```
**d.YV12 To NV12**
```cpp
void yv12ToNV12(unsigned char* yv12, unsigned  char* nv12, int width, int height)
{
    unsigned char* y_yv12 = yv12;
    unsigned char* v_yv12 = yv12 + width*height;
    unsigned char* u_yv12 = yv12 + width*height + width*height / 4;

unsigned char* y_nv12 = nv12;
    unsigned char* u_nv12 = nv12 + width*height;
    unsigned char* v_nv12 = nv12 + width*height + 1;

memcpy(nv12, yv12, width*height);

for (int i = 0; i < width*height / 4; ++i)
    {
        *v_nv12 = *v_yv12;
        *u_nv12 = *u_yv12;

v_nv12 += 2;
        u_nv12 += 2;

++v_yv12;
        ++u_yv12;
    }
}
```

**e.YV12 To YUYV**
```cpp
void yv12ToYUYV(unsigned char* yv12, unsigned char* yuyv, int width, int height)
{
    unsigned char* y_yv12 = yv12;
    unsigned char* v_yv12 = yv12 + width*height;
    unsigned char* u_yv12 = yv12 + width*height + width*height / 4;

unsigned char* y_yuyv = yuyv;
    unsigned char* u_yuyv = yuyv + 1;
    unsigned char* v_yuyv = yuyv + 3;

for (int i = 0; i < width; ++i)
    {
        for (int j = 0; j < height; ++j)
        {
            *y_yuyv = *y_yv12;

y_yuyv += 2;
            ++y_yv12;
        }
    }

for (int j = 0; j < height / 2; ++j)
    {
        for (int i = 0; i < width / 2; ++i)
        {
            *u_yuyv = *u_yv12;
            *(u_yuyv + width * 2) = *u_yv12;
            u_yuyv += 4;
            ++u_yv12;

*v_yuyv = *v_yv12;
            *(v_yuyv + width * 2) = *v_yv12;
            v_yuyv += 4;
            ++v_yv12;
        }
        u_yuyv += width * 2;
        v_yuyv += width * 2;
    }
} 
```
虹软免费的sdk下载：https://ai.arcsoft.com.cn/product/arcface.html

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