DirectShow基础编程 最简单transform filter 编写步骤

目标编写一个transform filter，功能是对图像进行翻转。

一、选择基类

从CBaseFilter派生出三个用于编写transform filter的类，各自是：CTransformFilter 、CTransInPlaceFilter 和CVideoTransformFilter ，三个基类的差别能够看MSDN的说明，我们选择CTransformFilter类。

选择好基类，我们就创建一个空的DLLproject，加入三个文件，各自是：FlipFilter.h、FlipFilter.cpp和FlipFilter.def。

二、声明Filter类

在FlipFilter.h中加入下列代码声明

[cpp] view plaincopyprint?#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、媒体类型协商

这一步是Filter的pin在连接的时候必须进行的步骤。主要重载三个函数：

1、HRESULT CheckInputType(const CMediaType *mtIn);

[cpp] view plaincopyprint?

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类作为输入pin，CTransformInputPin::CheckMediaType(const CMediaType* pmt)中调用m_pTransformFilter->CheckInputType(pmt);因此我们能够简单的觉得CheckInputType就是输入pin的CheckMediaType。

这样设计的是为了不须要又一次定义输入pin类，仅仅须要定义Filter类。简化编写Transform filter的步骤，另外的几个接口也是这种一个设计原理。

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

[cpp] view plaincopyprint?

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;
}

相同的，这个函数也是为输入pin所写。

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

[cpp] view plaincopyprint?

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

return E_FAIL;
}

这个函数是输出pin调用。CTransformOutputPin::CheckMediaType(const CMediaType* pmtOut)中调用m_pTransformFilter->CheckTransform。

四、协商分配器的属性。决定数据的属性

[cpp] view plaincopyprint?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;
}

这个函数由CTransformOutputPin::DecideBufferSize调用。

五、实现数据转换

[cpp] view plaincopyprint" style="color: rgb(204, 204, 204); text-decoration: none; background-image: none; border: none; padding: 0px; margin: 0px 10px 0px 0px; font-size: 9px; background-position: initial initial; background-repeat: initial initial;">?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);

//翻转图像
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、加入COM信息，使DLL成为filter

1、创建filter实例。这是标准格式

[cpp] view plaincopyprint?

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、声明工厂类模版

[cpp] view plaincopyprint?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、注冊和注销filter，DLL的全局入口

[cpp] view plaincopyprint" style="color: rgb(204, 204, 204); text-decoration: none; background-image: none; border: none; padding: 0px; margin: 0px 10px 0px 0px; font-size: 9px; background-position: initial initial; background-repeat: initial initial;">?

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编写完毕。