GMC Question

[ChronoCross]

When Encoding using GMC then playing it in MPC using the OSD from FDDshow it prints a pattern like the following example BPBGMCPB

My Question is. Are GMC frames bigger, smaller, or the same as B frames. and technically what is the benefit of having GMC enabled. Does having a GMC frame in there in anyway adversely affect Bframe quality? Thanks in advance.

[Tommy Carrot]

GMC has practically nothing to do with b-frames, it's a completely different animal. The GMC is used during the normal P-frame prediction. If applying the global motion compensation makes a particular frame smaller, it'll become GMC'ed p-frame (s-frame, if i remeber correctly), if not, it'll remain normal p-frame.