PS 2.0 bicubic resizing cpu usage

[breez]

Why does the PS 2.0 resizing option in MPC take such a large CPU hit when it is done in hardware?

Ffdshow (20051109) decoding a ~900kbps xvid (640x480)
mplayer deblocking (accurate)
HQ RGB32 conversion
VMR9 renderless

On a 1.9GHz Athlon XP the above takes around 40% and when resized to fullscreen (1024x768) the cpu usage shoots to 80%! The video card used is a Radeon 9800Pro AIW.

[breez]

Ahaa, found a solution. When "Lock back buffer before presenting (may fix broken vertical synconization)" is unchecked the CPU usage stays at the same level regardless of resizing. If I'd have to throw a guess, the stuff is transferred back from video card to do the thing which would cause extra CPU stress.