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DirectShow 驅動攝影機完整實作：簡易版捕獲與預覽

編輯：關於VC++

DirectShow 驅動攝影機靈活性佳，支援 WDM 驅動與舊版驅動。本文介紹簡易版實作：建立濾鏡圖、列舉裝置、連接預覽腳位、設定視訊視窗。

核心 COM 介面

IGraphBuilder：建立濾鏡圖
ICaptureGraphBuilder2：連接捕獲裝置與下游濾鏡
IVideoWindow：控制視訊視窗屬性
IMediaControl：控制執行/停止/暫停
IMediaEventEx：事件通知處理

完整初始化代碼


CComQIPtr m_pVW;
CComQIPtr m_pMC;
CComQIPtr m_pME;
CComPtr m_pGraph;
CComPtr m_pCapture;
DWORD m_dwGraphRegister;

bool bInit(HWND hWnd) {
    HRESULT hr;
    // 1. 建立核心介面
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC,
        IID_IGraphBuilder, (void**)&m_pGraph);
    if (FAILED(hr)) return false;

    hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, CLSCTX_INPROC,
        IID_ICaptureGraphBuilder2, (void**)&m_pCapture);
    if (FAILED(hr)) return false;

    m_pMC = m_pGraph;
    m_pVW = m_pGraph;
    m_pME = m_pGraph;

    // 2. 事件通知視窗
    m_pME->SetNotifyWindow((OAHWND)hWnd, WM_GRAPHNOTIFY, 0);

    // 3. 連接捕獲建構器與濾鏡圖
    m_pCapture->SetFiltergraph(m_pGraph);

    // 4. 列舉視訊輸入裝置
    CComPtr pCde;
    CComPtr pEm;
    hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC,
        IID_ICreateDevEnum, (void**)&pCde);
    if (FAILED(hr)) return false;

    pCde->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pEm, 0);
    if (pEm == NULL) return false;

    CComPtr pM;
    ULONG cFetched;
    CComPtr pBf;
    if (pEm->Next(1, &pM, &cFetched) == S_OK) {
        pM->BindToObject(0, 0, IID_IBaseFilter, (void**)&pBf);
        pM.Release();
    } else return false;

    // 5. 將裝置加入濾鏡圖
    hr = m_pGraph->AddFilter(pBf, L"Video Capture");
    if (FAILED(hr)) return false;

    // 6. 連接預覽腳位
    hr = m_pCapture->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video,
        pBf, NULL, NULL);
    if (FAILED(hr)) return false;
    pBf.Release();

    // 7. 設定視訊視窗
    hr = m_pVW->put_Owner((OAHWND)hWnd);
    if (FAILED(hr)) return false;
    m_pVW->put_WindowStyle(WS_CHILD | WS_CLIPCHILDREN);
    if (FAILED(hr)) return false;

    CRect rectClient;
    GetClientRect(hWnd, &rectClient);
    m_pVW->SetWindowPosition(0, 0, 320, 240);  // 固定尺寸

    hr = m_pVW->put_Visible(OATRUE);
    if (FAILED(hr)) return false;

    // 8. 註冊至執行中物件表 (ROT) 供遠端除錯
    CComPtr pROT;
    GetRunningObjectTable(0, &pROT);
    WCHAR c[128];
    wsprintfW(c, L"FilterGraph %08x pid %08x\0",
        (DWORD_PTR)m_pGraph.p, GetCurrentProcessId());
    CComPtr pMoniker;
    hr = CreateItemMoniker(L"!", c, &pMoniker);
    if (FAILED(hr)) return false;
    hr = pROT->Register(ROTFLAGS_REGISTRATIONKEEPSALIVE,
        m_pGraph, pMoniker, &m_dwGraphRegister);
    pMoniker.Release();

    return true;
}