解码YUV的filter

求助解码YUV的filter
最近在写一个解码yuv的transform filter，文件为.yuv格式，视频大小为320*240，内容为YYYY...Y共320*240个，UUUU..U共160*120个，VVVV...V共160*120.由于不想写SourceFilter，就用系统自带的一个叫做：File Source（Async.）的Source Filter，但是在GraphEdit中调试时，一连线就停止工作，debug时看到Source Filter传过来的视频格式为MEDIATYPE_NULL，和MEDIASUBTYPE_NULL，这样一步一步的调试也不知道哪出了问题，希望大家能帮我一下，谢谢！
下面是大概的源代码
#include <windows.h>
#include <streams.h>
#include <initguid.h>
#include <olectl.h>
#include <fstream>
#include "Decoder.h"

const AMOVIESETUP_MEDIATYPE sudPinTypes=
{
&MEDIATYPE_NULL,
&MEDIASUBTYPE_NULL
};

const AMOVIESETUP_MEDIATYPE outputpinType=
{
&MEDIATYPE_Video,
&MEDIASUBTYPE_NULL
};

const AMOVIESETUP_PIN sudPins[]=
{
{
L"Input", // Pins string name
FALSE, // Is it rendered
FALSE, // Is it an output
FALSE, // Are we allowed none
FALSE, // And allowed many
&CLSID_NULL, // Connects to filter
NULL, // Connects to pin
1, // Number of types
&sudPinTypes // Pin information
},
{
L"Output", // Pins string name
FALSE, // Is it rendered
TRUE, // Is it an output
FALSE, // Are we allowed none
FALSE, // And allowed many
&CLSID_NULL, // Connects to filter
NULL, // Connects to pin
1, // Number of types
&outputpinType // Pin information
}
};

const AMOVIESETUP_FILTER sudDecoder=
{
&CLSID_Decoder, // Filter CLSID
L"A test Decoder", // String name
MERIT_PREFERRED, // Filter merit
2, // Number of pins
sudPins // Pin information
};

CFactoryTemplate g_Templates[]=
{
{
L"A Test Decoder",
&CLSID_Decoder,
Decoder::CreateInstance,
NULL,
&sudDecoder
}
};

int g_cTemplates=sizeof(g_Templates)/sizeof(g_Templates[0]);

STDAPI DllRegisterServer()
{
return AMovieDllRegisterServer2(TRUE);
}

STDAPI DllUnregisterServer()
{
return AMovieDllRegisterServer2(FALSE);
}

extern "C" BOOL WINAPI DllEntryPoint(HINSTANCE, ULONG, LPVOID);

//
// DllMain
//
BOOL APIENTRY DllMain(HANDLE hModule,DWORD dwReason,LPVOID lpReserved)
{
return DllEntryPoint((HINSTANCE)(hModule),dwReason,lpReserved);
}

//
// Debug
//
void Debuginfo(char *info)
{
FILE *pf;
fopen_s(&pf,"C:\\debug.txt","a+");
fprintf(pf,info);
fclose(pf);
}

Decoder::Decoder(TCHAR *tszName,LPUNKNOWN punk,HRESULT *phr):CTransformFilter(tszName, punk, CLSID_Decoder),fillnum(0),samplesize(115200),startTime(0)
{
buffers=(unsigned char *)malloc(1048576);//1048576:pow(2,20)
if(!buffers)
exit(-1);
}

Decoder::~Decoder()
{
free(buffers);
}

//
// CreateInstance
//
CUnknown *Decoder::CreateInstance(LPUNKNOWN punk, HRESULT *phr)
{
ASSERT(phr);
Debuginfo("now create an intance\n");
Decoder *pNewObject=new Decoder(NAME("A Test Decoder"), punk, phr);
  if (pNewObject == NULL)
{
if (phr)
*phr = E_OUTOFMEMORY;
  }
  return pNewObject;
}

STDMETHODIMP Decoder::NonDelegatingQueryInterface(REFIID riid, void **ppv)
{
CheckPointer(ppv,E_POINTER);
return CTransformFilter::NonDelegatingQueryInterface(riid, ppv);
}

//
// Transform
//
HRESULT Decoder::Transform(IMediaSample *pIn, IMediaSample *pOut)
{
Debuginfo("in Transform\n");
CheckPointer(pIn,E_POINTER);
CheckPointer(pOut,E_POINTER);
Debuginfo("in Transform\n");
BYTE *pSourceBuffer,*pDestBuffer;