Hi jmorrill and Kenneta
Thanks for your feedbacks. I have surveyed this issue for few days.
It seems VMR9 don't support ARGB32 format for mixing. VMR9 only support fixed alpha value or AlphaBitmap.
I try to render ARGB32 to VMR9 filter and it can't be connected.
So it seems it's not related to MediaKit issue, it's VMR9's limitation.
But I can share some conclusion of my investigation.
Goal --> overlay videos with alpha channel together.
Support Video Codec with alpha Channel -->
MOVs (at least TGA inside) --> but it's not directshow based, and I can't find any 3 party direct-show filter to playback MOV with TGA format inside (RGBA)
FLV --> in default, it seems it will be decode to RGB, i try to use FLV decoder filter and i can decode RGBA, but VMR9 can't get it
Uncompressed AVI --> the information is from internet, but i haven't try because VMR9 doesn't work!
I try to use any technology to achieve. (WPF, XNA, DirectShow, with D3dimage, ...etc)
It seems so far there's no good and easy way to achieve my goal.
I try to decode series of PNG with alpha channel to act as video, but the frame rate is not easy to achieve 25 FPS and also depends on hardware.
Color Key or Color Range by using PixelShader (in WPF, XNA, ...etc) might be a alternative way, but the overall quality can't compete to true alpha channel.
:-( But thanks for your precious suggestions.