I have noticed that on some clips, the deblocking filters (pp=hb/vb) will make blocking worse. For example, on the Evangelion Perfect Collection DVDs, enabling the deblocking filters will cause both more visible blocking and rapid noise as these blocks shift between slightly different luminances. But I noticed that if you compile mplayer without mmx/mmx2/sse support (I have a P3 so those are what it will use), the deblocking filter then doesn't cause this. I have made a small AVI of the first seven seconds of the first episode, this contains a scene (red plasma with the studio's name) where this is unusually obvious. I made it using mencoder's -ovc copy option so it's exactly what's on the DVD. It's at http://jc4.rh.ncsu.edu/local/evaintro.avi