DirectShow基礎編程 最簡單transform filter 編寫步驟

目標編寫一個transform filter，功能是對圖像進行翻轉。

MSDN中有一章 "Writing Transform Filters" 列出了編寫transform filter的六個基本步驟，我們按照這六個步驟一步一步來。

 

一、選擇基類

從CBaseFilter派生出三個用於編寫transform filter的類，分別是：CTransformFilter 、CTransInPlaceFilter 和CVideoTransformFilter ，三個基類的區別可以看MSDN的說明，我們選擇CTransformFilter類。

選擇好基類，我們就創建一個空的DLL工程，添加三個文件，分別是：FlipFilter.h、FlipFilter.cpp和FlipFilter.def。

 

二、聲明Filter類

在FlipFilter.h中添加下列代碼聲明

#include <streams.h> extern "C" const GUID CLSID_FlipFilter; class CFlipFilter : public CTransformFilter { private: CFlipFilter(TCHAR *tszName, LPUNKNOWN punk, HRESULT *phr); public: static CUnknown * WINAPI CreateInstance(LPUNKNOWN punk, HRESULT *phr); HRESULT CheckInputType(const CMediaType *mtIn); HRESULT GetMediaType(int iPosition, CMediaType *pMediaType); HRESULT CheckTransform(const CMediaType *mtIn, const CMediaType *mtOut); HRESULT DecideBufferSize(IMemAllocator * pAllocator, ALLOCATOR_PROPERTIES *pprop); HRESULT Transform(IMediaSample *pIn, IMediaSample *pOut); };

 

三、媒體類型協商

這一步是Filter的pin在連接的時候必須進行的步驟，主要重載三個函數：

1、HRESULT CheckInputType(const CMediaType *mtIn);

HRESULT CFlipFilter::CheckInputType(const CMediaType *mtIn) { if (mtIn->majortype != MEDIATYPE_Video || mtIn->subtype != MEDIASUBTYPE_RGB24 || mtIn->formattype != FORMAT_VideoInfo ) { return VFW_E_TYPE_NOT_ACCEPTED; } VIDEOINFO* pvi = (VIDEOINFO*)mtIn->Format(); if (pvi->bmiHeader.biBitCount != 24) { return VFW_E_TYPE_NOT_ACCEPTED; } return S_OK; }

CTransformFilter使用CTransformInputPin類作爲輸入pin，CTransformInputPin::CheckMediaType(const CMediaType* pmt)中調用m_pTransformFilter->CheckInputType(pmt);因此我們可以簡單的認爲CheckInputType就是輸入pin的CheckMediaType。這樣設計的是爲了不需要重新定義輸入pin類，只需要定義Filter類，簡化編寫Transform filter的步驟，另外的幾個接口也是這樣的一個設計原理。

2、HRESULT GetMediaType(int iPosition, CMediaType *pMediaType);

HRESULT CFlipFilter::GetMediaType(int iPosition, CMediaType *pMediaType) { if (m_pInput->IsConnected() == FALSE) { return E_UNEXPECTED; } if (iPosition < 0) { return E_INVALIDARG; } if (iPosition > 0) { return VFW_S_NO_MORE_ITEMS; } CheckPointer(pMediaType,E_POINTER); *pMediaType = m_pInput->CurrentMediaType(); return NOERROR; }

同樣的，這個函數也是爲輸入pin所寫。

3、HRESULT CheckTransform(const CMediaType *mtIn, const CMediaType *mtOut);

HRESULT CFlipFilter::CheckTransform(const CMediaType *mtIn, const CMediaType *mtOut) { if (*mtIn == *mtOut) { return NOERROR; } return E_FAIL; }

這個函數是輸出pin調用。CTransformOutputPin::CheckMediaType(const CMediaType* pmtOut)中調用m_pTransformFilter->CheckTransform。

 

四、協商分配器的屬性，決定數據的屬性

HRESULT CFlipFilter::DecideBufferSize(IMemAllocator * pAllocator, ALLOCATOR_PROPERTIES *pprop) { if (m_pInput->IsConnected() == FALSE) { return E_UNEXPECTED; } CheckPointer(pAllocator,E_POINTER); CheckPointer(pprop,E_POINTER); HRESULT hr = NOERROR; pprop->cBuffers = 1; pprop->cbBuffer = m_pInput->CurrentMediaType().GetSampleSize(); ASSERT(pprop->cbBuffer); ALLOCATOR_PROPERTIES Actual; hr = pAllocator->SetProperties(pprop,&Actual); if (FAILED(hr)) { return hr; } ASSERT( Actual.cBuffers == 1 ); if (pprop->cBuffers > Actual.cBuffers || pprop->cbBuffer > Actual.cbBuffer) { return E_FAIL; } return NOERROR; }

這個函數由CTransformOutputPin::DecideBufferSize調用。

 

五、實現數據轉換

HRESULT CFlipFilter::Transform(IMediaSample *pIn, IMediaSample *pOut) { CheckPointer(pIn,E_POINTER); CheckPointer(pOut,E_POINTER); BYTE *pSourceBuffer, *pDestBuffer; long lSourceSize = pIn->GetActualDataLength(); pIn->GetPointer(&pSourceBuffer); pOut->GetPointer(&pDestBuffer); //翻轉圖像 CMediaType pMediaType1 = m_pInput->CurrentMediaType(); VIDEOINFOHEADER* pvi = (VIDEOINFOHEADER*)pMediaType1.pbFormat; int nWidth = WIDTHBYTES(pvi->bmiHeader.biWidth * pvi->bmiHeader.biBitCount); for (int i = 0; i < pvi->bmiHeader.biHeight; i ++) { CopyMemory((PVOID) (pDestBuffer + nWidth * i), (PVOID) (pSourceBuffer + nWidth * (pvi->bmiHeader.biHeight - i - 1)), nWidth); } REFERENCE_TIME TimeStart, TimeEnd; if(NOERROR == pIn->GetTime(&TimeStart, &TimeEnd)) { pOut->SetTime(&TimeStart, &TimeEnd); } LONGLONG MediaStart, MediaEnd; if(pIn->GetMediaTime(&MediaStart,&MediaEnd) == NOERROR) { pOut->SetMediaTime(&MediaStart,&MediaEnd); } HRESULT hr = pIn->IsSyncPoint(); if(hr == S_OK) { pOut->SetSyncPoint(TRUE); } else if(hr == S_FALSE) { pOut->SetSyncPoint(FALSE); } else { return E_UNEXPECTED; } hr = pIn->IsPreroll(); if(hr == S_OK) { pOut->SetPreroll(TRUE); } else if(hr == S_FALSE) { pOut->SetPreroll(FALSE); } else { return E_UNEXPECTED; } hr = pIn->IsDiscontinuity(); if(hr == S_OK) { pOut->SetDiscontinuity(TRUE); } else if(hr == S_FALSE) { pOut->SetDiscontinuity(FALSE); } else { return E_UNEXPECTED; } long lDataLength = pIn->GetActualDataLength(); pOut->SetActualDataLength(lDataLength); return NOERROR; }

 

六、添加COM信息，使DLL成爲filter

1、創建filter實例，這是標準格式

CUnknown* CFlipFilter::CreateInstance(LPUNKNOWN punk, HRESULT *phr) { ASSERT(phr); CFlipFilter *pNewObject = new CFlipFilter(NAME("FlipFilter"), punk, phr); if (pNewObject == NULL) { if (phr) *phr = E_OUTOFMEMORY; } return pNewObject; }

2、聲明工廠類模版

const AMOVIESETUP_MEDIATYPE sudInputPinTypes = { &MEDIATYPE_Video, &MEDIASUBTYPE_NULL }; const AMOVIESETUP_MEDIATYPE sudOutputPinTypes = { &MEDIATYPE_Video, &MEDIASUBTYPE_NULL }; const AMOVIESETUP_PIN sudpPins[] = { { L"Input", FALSE, FALSE, FALSE, FALSE, &CLSID_NULL, NULL, 1, &sudInputPinTypes }, { L"Output", FALSE, TRUE, FALSE, FALSE, &CLSID_NULL, NULL, 1, &sudOutputPinTypes } }; const AMOVIESETUP_FILTER sudFlipFilter = { &CLSID_FlipFilter, L"FlipFilter", MERIT_DO_NOT_USE, 2, sudpPins }; CFactoryTemplate g_Templates[] = { { L"FlipFilter" , &CLSID_FlipFilter , CFlipFilter::CreateInstance , NULL , &sudFlipFilter } }; int g_cTemplates = sizeof(g_Templates) / sizeof(g_Templates[0]); REGFILTER2 rf2FilterReg = { 1, MERIT_DO_NOT_USE, 2, sudpPins };

3、註冊和註銷filter，DLL的全局入口

BOOL APIENTRY DllMain(HANDLE hModule, DWORD dwReason, LPVOID lpReserved) { return DllEntryPoint((HINSTANCE)(hModule), dwReason, lpReserved); } STDAPI DllRegisterServer() { return AMovieDllRegisterServer2( TRUE ); } STDAPI DllUnregisterServer() { return AMovieDllRegisterServer2( FALSE ); }

 

Filter編寫完成。

 

注：完整代碼下載：http://d.download.csdn.net/down/2435821/bwmwm