Identify the KeyFrame in a compressed input pin Filter

I developed the Netwriter Filter which accepts input as
Windows Media video.

within Netwriter Filter, how can we identify the KeyFrame ?

WMV is a compressed Format. How can we identify the Key Frame?

if the input pin of the transform filter is in compressed format,
How can we identify the KeyFrame ?...



Solution:
-----------

Using IMediaSample's IsSyncPoint() fn.

IsSyncPoint() fn returns S_OK if it is a KeyFrame.

otherwise it returns S_FALSE;


In Directshow, The technical name for the KeyFrame is Synchronization Point.
So we checked it as

IsSyncPoint ()