IMediaSeeking::GetCurrentPosition always returns 0. Why?

[diandaolly]

I used below graph to convert WMA to Wave in DirectShow:
------
WM ASF Reader -> WMA Decoder -> WavDest -> File Writer
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The conversion is OK. I did get my wav file.

To However, I'd like to use IMediaSeeking::GetCurrentPosition()/
GetDuration() to indicate the conversion progress.

I successfully obtained the IMediaSeeking interface from the output
pin of WavDest.
Before running the graph, I can also get the duration time.

However, no matter the graph is running or not,
when I call IMediaSeeking::GetCurrentPosition(),
I always get "zero".

Why? Please help. TIA.

[diandaolly]

BTW, I got the hint from this post:
http://www.eggheadcafe.com/software/aspnet/35996086/getting-progress-of-a-des-timeline-rendering-with-only-audio.aspx

Pity it does not work for me.