DirectShow SetPositions not working

Hi.
I am a beginner with Directshow. I am trying to play specific portion of a given video clip
(say in a 100sec clip I want to play from 20-40 seconds).This is the main portion of the code that I use:

CoCreateInstance(CLSID_FilterGraph,NULL,CLSCTX_INPROC,IID_IGraphBuilder,(LPVOID*)&pGraphBuilder);

pGraphBuilder->QueryInterface(IID_IMediaControl,(LPVOID*)&pMediaControl);
pGraphBuilder->QueryInterface(IID_IMediaEvent,(LPVOID*)&pMediaEvent);
pGraphBuilder->QueryInterface(IID_IMediaSeeking,(LPVOID*)&pMediaSeeking);
double length;
pMediaControl->RenderFile(FILENAME);
IMediaPosition *pMediaPosition;
pGraphBuilder->QueryInterface(IID_IMediaPosition,(LPVOID*)&pMediaPosition);
pMediaPosition->get_Duration(&length);
pGraphBuilder->QueryInterface(IID_IVideoWindow,(LPVOID*)&pVideoWindow);

LONGLONG start=20;
LONGLONG stop=60;
HRESULT hr=pMediaSeeking->SetPositions(&start,AM_SEEKING_AbsolutePositioning,&stop,AM_SEEKING_AbsolutePositioning);

pMediaControl->Run();


I set a breakpoint and check the value of hr which is S_OK.But the video does not play ...only a blank video window shows up.



Can anybody help me with this?

Did you CheckCapabilities about absolute seeking?

Besides, what is the current time format?

Quote:

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IMediaSeeking::SetPositions Method
Parameters
pCurrent [in, out]

[in,out] Pointer to a variable that specifies the current position, in units of the current time format.

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Quote:

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Time Format GUIDs
TIME_FORMAT_MEDIA_TIME Reference time (100-nanosecond units).

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Quote:

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(say in a 100sec clip I want to play from 20-40 seconds)

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Code:

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const QWORD QW_SECOND = 10000000;
LONGLONG start = 20 * QW_SECOND;
LONGLONG stop = 60 * QW_SECOND;

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I did check that out.Actually I am using the following graph

Source Filter->AVI mux->File Writer

and perhaps because of the AVI mux the setpositions method of IMediaSeeking returns a E_NOTIMPL.I am confused now how to implement this.