编写代码对接海康威视的视频预览

对接海康威视的视频预览需要使用海康威视提供的 SDK，以下是一个简单的代码示例：

#include "stdafx.h"
#include "HCNetSDK.h"
#include "PlayM4.h"

#pragma comment(lib, "HCNetSDK.lib")
#pragma comment(lib, "PlayCtrl.lib")

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);

int main()
{
    NET_DVR_Init();
    NET_DVR_SetConnectTime(2000, 1);
    NET_DVR_SetReconnect(10000, true);

    NET_DVR_DEVICEINFO_V30 deviceInfo;
    LONG lUserID = NET_DVR_Login_V30("192.168.1.64", 8000, "admin", "12345", &deviceInfo);
    if (lUserID < 0)
    {
        printf("Login failed. Error code: %d\n", NET_DVR_GetLastError());
        NET_DVR_Cleanup();
        return 0;
    }

    NET_DVR_CLIENTINFO clientInfo = { 0 };
    clientInfo.lChannel = 1;
    clientInfo.lLinkMode = 0;
    clientInfo.hPlayWnd = NULL;
    clientInfo.sMultiCastIP = NULL;

    LONG lRealPlayHandle = NET_DVR_RealPlay_V30(lUserID, &clientInfo, NULL, NULL, true);
    if (lRealPlayHandle < 0)
    {
        printf("Real play failed. Error code: %d\n", NET_DVR_GetLastError());
        NET_DVR_Logout(lUserID);
        NET_DVR_Cleanup();
        return 0;
    }

    HWND hWnd = ::CreateWindowEx(WS_EX_TRANSPARENT, TEXT("static"), NULL, WS_CHILD | WS_VISIBLE, 0, 0, 640, 480, NULL, NULL, ::GetModuleHandle(NULL), NULL);
    ::SetWindowLong(hWnd, GWL_WNDPROC, (LONG)WndProc);
    ::ShowWindow(hWnd, SW_SHOW);

    HWND hPlayWnd = ::GetDlgItem(hWnd, 0);
    ::PlayM4_SetDisplayBuf(0);

    if (!::PlayM4_Play(hPlayWnd, lRealPlayHandle))
    {
        printf("Play failed. Error code: %d\n", ::PlayM4_GetLastError(lRealPlayHandle));
        NET_DVR_StopRealPlay(lRealPlayHandle);
        NET_DVR_Logout(lUserID);
        NET_DVR_Cleanup();
        return 0;
    }

    MSG msg;
    while (::GetMessage(&msg, NULL, 0, 0))
    {
        ::TranslateMessage(&msg);
        ::DispatchMessage(&msg);
    }

    ::PlayM4_Stop(lRealPlayHandle);
    ::PlayM4_CloseStream(lRealPlayHandle);
    NET_DVR_StopRealPlay(lRealPlayHandle);
    NET_DVR_Logout(lUserID);
    NET_DVR_Cleanup();

    return 0;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    switch (message)
    {
    case WM_DESTROY:
        ::PostQuitMessage(0);
        break;
    default:
        return ::DefWindowProc(hWnd, message, wParam, lParam);
    }

    return 0;
}

这段代码使用了海康威视提供的 SDK 连接到一个设备，并将设备的实时视频预览在窗口中显示。其中需要注意的是，这段代码使用了 Windows API 创建了一个窗口，并将实时视频渲染到该窗口中。你需要将代码中的设备 IP、用户名和密码修改为实际的值，同时也需要根据自己的需求修改窗口大小等参数。