在 DirectShow 中保持纵横比？（窗口）C++

Question

编辑：更新了代码，调用 DLL 的应用程序不再崩溃。

我希望 DirectShow 播放的视频在 show_video() 的第四个参数设置为 true 时保持其纵横比。这是我的 DLL 源代码：

#include <windows.h>
#include <dshow.h>

#pragma comment (lib, "strmiids.lib")
#define DLL extern "C" _declspec(dllexport)

wchar_t *convertCharArrayToLPCWSTR(const char* charArray) {
    wchar_t* wString = new wchar_t[4096];

    MultiByteToWideChar(CP_ACP, 0, charArray, -1, wString, 4096);

    return wString;
}

DLL void show_video(double window1, HWND window2, char *fname, double keep_aspect_ratio) {
    CoInitialize(NULL);

    HRESULT hr = S_OK;

    IGraphBuilder *pGraph = NULL;
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);
    hr = pGraph->RenderFile(convertCharArrayToLPCWSTR(fname), NULL);

    IBaseFilter *pVideoRenderer = NULL;
    hr = CoCreateInstance(CLSID_VideoMixingRenderer, NULL, CLSCTX_INPROC_SERVER, IID_IBaseFilter, (void **)&pVideoRenderer);

    IVMRAspectRatioControl *pAspectRatio = NULL;
    hr = pVideoRenderer->QueryInterface(IID_IVMRAspectRatioControl, (void**)&pAspectRatio);

    if ((bool)keep_aspect_ratio == true) {
        hr = pAspectRatio->SetAspectRatioMode(VMR_ARMODE_LETTER_BOX);
    }
    else {
        hr = pAspectRatio->SetAspectRatioMode(VMR_ARMODE_NONE);
    }

    IVideoWindow *pVidWin = NULL;
    hr = pGraph->QueryInterface(IID_IVideoWindow, (void **)&pVidWin);

    RECT rect;
    if ((HWND)(DWORD)window1 != NULL) {
        SetWindowLong((HWND)(DWORD)window1, GWL_STYLE, GetWindowLong((HWND)(DWORD)window1, GWL_STYLE) | WS_CLIPCHILDREN | WS_CLIPSIBLINGS);
        hr = pVidWin->put_Owner((OAHWND)(HWND)(DWORD)window1);
        GetClientRect((HWND)(DWORD)window1, &rect);
    }
    else {
        SetWindowLong(window2, GWL_STYLE, GetWindowLong(window2, GWL_STYLE) | WS_CLIPCHILDREN | WS_CLIPSIBLINGS);
        hr = pVidWin->put_Owner((OAHWND)window2);
        GetClientRect(window2, &rect);
    }

    hr = pVidWin->SetWindowPosition(0, 0, rect.right - rect.left, rect.bottom - rect.top);
    hr = pVidWin->put_WindowStyle(WS_CHILD | WS_CLIPSIBLINGS);
    hr = pVidWin->SetWindowForeground(OATRUE);
    hr = pVidWin->HideCursor(OATRUE);

    IMediaControl *pControl = NULL;
    hr = pGraph->QueryInterface(IID_IMediaControl, (void**)&pControl);
    hr = pControl->Run();

    IMediaEvent *pEvent = NULL;
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
    long evCode;

    hr = pEvent->WaitForCompletion(INFINITE, &evCode);

    hr = pControl->Stop();
    hr = pVidWin->put_Visible(OAFALSE);
    hr = pVidWin->put_Owner(NULL);

    pEvent->Release();
    pControl->Release();
    pVidWin->Release();

    pAspectRatio->Release();
    pVideoRenderer->Release();
    pGraph->Release();

    CoUninitialize();
}

就目前而言，从我的应用程序调用 DLL，我为第三个参数选择的视频播放正常，但视频没有保持其原始宽高比。有谁知道我做错了什么？

Answer 1

...the process calling the DLL now crashes.

进程崩溃假设您可以提供额外的详细信息，如崩溃点、异常详细信息等。

可能的原因是 E_NOINTERFACE 前面的 QueryInterface 调用失败并且缺少 IVMRAspectRatioControl 指针。

Filter Graph Manager 不应该实现 IVMRAspectRatioControl。如果您的过滤器图表中有视频混合渲染器过滤器，QueryInterface 直接来自它。

更新。另一个答案中的解决方案是不应该如何做的一个例子。如果你为 VR 做 CoCreateInstance，你应该把它添加到图形中，并将它包含到渲染过程中。否则，您根本不需要 CoCreateInstance，并且您不应该按名称定位过滤器 - 而是枚举过滤器并通过查找实现相关接口的过滤器来识别您的 VR。

Answer 2

找到解决方案。初始化 pVideoRenderer 后，我需要添加以下行：

pGraph->FindFilterByName(L"Video Renderer", &pVideoRenderer);

因此生成的代码如下所示：

#include <windows.h>
#include <dshow.h>

#pragma comment (lib, "strmiids.lib")
#define DLL extern "C" _declspec(dllexport)

wchar_t *convertCharArrayToLPCWSTR(const char* charArray) {
    wchar_t* wString = new wchar_t[4096];

    MultiByteToWideChar(CP_ACP, 0, charArray, -1, wString, 4096);

    return wString;
}

DLL void show_video(double window1, HWND window2, char *fname, double keep_aspect_ratio) {
    CoInitialize(NULL);

    HRESULT hr = S_OK;

    IGraphBuilder *pGraph = NULL;
    hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER, IID_IGraphBuilder, (void **)&pGraph);
    hr = pGraph->RenderFile(convertCharArrayToLPCWSTR(fname), NULL);

    IBaseFilter *pVideoRenderer = NULL;
    hr = CoCreateInstance(CLSID_VideoMixingRenderer, NULL, CLSCTX_INPROC_SERVER, IID_IBaseFilter, (void **)&pVideoRenderer);
    pGraph->FindFilterByName(L"Video Renderer", &pVideoRenderer);

    IVMRAspectRatioControl *pAspectRatio = NULL;
    hr = pVideoRenderer->QueryInterface(IID_IVMRAspectRatioControl, (void**)&pAspectRatio);

    if ((bool)keep_aspect_ratio == true) {
        hr = pAspectRatio->SetAspectRatioMode(VMR_ARMODE_LETTER_BOX);
    }
    else {
        hr = pAspectRatio->SetAspectRatioMode(VMR_ARMODE_NONE);
    }

    IVideoWindow *pVidWin = NULL;
    hr = pGraph->QueryInterface(IID_IVideoWindow, (void **)&pVidWin);

    RECT rect;
    if ((HWND)(DWORD)window1 != NULL) {
        SetWindowLong((HWND)(DWORD)window1, GWL_STYLE, GetWindowLong((HWND)(DWORD)window1, GWL_STYLE) | WS_CLIPCHILDREN | WS_CLIPSIBLINGS);
        hr = pVidWin->put_Owner((OAHWND)(HWND)(DWORD)window1);
        GetClientRect((HWND)(DWORD)window1, &rect);
    }
    else {
        SetWindowLong(window2, GWL_STYLE, GetWindowLong(window2, GWL_STYLE) | WS_CLIPCHILDREN | WS_CLIPSIBLINGS);
        hr = pVidWin->put_Owner((OAHWND)window2);
        GetClientRect(window2, &rect);
    }

    hr = pVidWin->SetWindowPosition(0, 0, rect.right - rect.left, rect.bottom - rect.top);
    hr = pVidWin->put_WindowStyle(WS_CHILD | WS_CLIPSIBLINGS);
    hr = pVidWin->SetWindowForeground(OATRUE);
    hr = pVidWin->HideCursor(OATRUE);

    IMediaControl *pControl = NULL;
    hr = pGraph->QueryInterface(IID_IMediaControl, (void**)&pControl);
    hr = pControl->Run();

    IMediaEvent *pEvent = NULL;
    hr = pGraph->QueryInterface(IID_IMediaEvent, (void **)&pEvent);
    long evCode;

    hr = pEvent->WaitForCompletion(INFINITE, &evCode);

    hr = pControl->Stop();
    hr = pVidWin->put_Visible(OAFALSE);
    hr = pVidWin->put_Owner(NULL);

    pEvent->Release();
    pControl->Release();
    pVidWin->Release();

    pAspectRatio->Release();
    pVideoRenderer->Release();
    pGraph->Release();

    CoUninitialize();
}

问题解决了！ :D

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