It's just normal banding and block artifacts from heavily compressed MPEG2 video (it's UK Freeview CH4+1 I think - AFAIK that channel is only 544 x 576 resolution and low bitrate, so I'm not surprised it looks like that....your GPUs noise filter might improve it, or the FFDShow video 'deband' filter works quite well)
Tony
Yeah, it is Ch4+1.
OK, perhaps STB use some filter to reduce the appearance of these artifacts, judging by some comments from people who say they don't see these on their STB.
I'll try the FFDShow deband filter but I'm using LAV and I'm not sure how to add ffdshow as a postprocessor. I've got ffdshow audio processor being used as a PP, but there's no ffdshow video processor, only ffdshow video decoder and raw video filter.