Audio/Video sync slip from track

See more:

C#

DirectX

directshow

.NET4

Hi all,
I am rendering a video in managed DirectX, using vmr9 and custom allocator.
Problem is audio/video are not in synchronization. I had also checked file in other players with no problem.
My findings: when i seek the position backward or forward solve the problem.
Hack that i found solve problem in some files but not for all. I had called WaitForCompletion() after run() on graph with timeOut of 100ms.
I dont have any idea why a/v sync slip from track.
Anyone know what going in there and have any idea plz share. Or anything i missed.
Thanks in advance.