keep aspect ratio in DirectShow? (windowed) C++ - c++

Question

EDIT: Updated the code and the application calling the DLL no longer crashes.
I want the video being played by DirectShow to keep its aspect ratio when the fourth argument of show_video() is set to true. Here's my DLL's source:
#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();
}
As it stands, calling the DLL from my application, the video I selected for the third argument plays fine, but the video does not keep its original aspect ratio. Does anyone know what I'm doing wrong?

Answer 1

Found the solution. After initializing pVideoRenderer, I needed to add the following line:
pGraph->FindFilterByName(L"Video Renderer", &pVideoRenderer);
So the resulting code looks like this:
#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();
}
Problem solved! :D

Answer 2

...the process calling the DLL now crashes.
A process crash supposes that you can provide additional details like crash point, exception details etc.
The likely cause is E_NOINTERFACE failure on the preceding QueryInterface call and absence of IVMRAspectRatioControl pointer.
Filter Graph Manager is not supposed to implement IVMRAspectRatioControl. If you have a Video Mixing Renderer filter in your filter graph, QueryInterface directly from it.
UPD. The solution in a another answer is an example of how things should not be done. If you do CoCreateInstance for VR, you should add it to the graph and include it to the rendering process. Otherwise, you don't need CoCreateInstance at all, and you should rather not locate filter by name - enumerate the filters instead and identify your VR by finding the filter which implements interface in question.