Hi Radek, since you seem to develop in windows you could easily "abuse" ffdshow to check whether you're doing things right, just use normal halfpel ME and add your GMC, set FourCC to DX50 - if it decodes correct you could assume your implementation is correct, too ;) (or use momusys decoder on raw bitstream...) Just a thought, maybe stupid, but I would test that way... Best regards, Koepi