Strange pixel effect in MPEG2

[tobenfun]

Why am I getting the following effect on MPEGs prepared for SVCD (as opposed to those for VCD which are perfect):
At certain times, where a degree motion is involved, the picture loses quality and there can be seen an effect asif the picture shown was an intense zoom; you can see square 'pixels'.
What is this, and how can I avoid it's happening?
Thanks,
Alan

[Tommyknocker]

You could soften block noise in TMPGEnc.

[wulf109]

the blocking is caused by low bitrate,high motion scenes require more bitrate. If you can't increase the bitrate try 2-passVBR,I find it is very effective at getting rid of macoblocking. Remember DVD is always encoded in VBR.

[tobenfun]

Thanks, guys, for the help. But I'm still not out of the woods yet.
I'm not encoding VBR. I'm encoding MPEG2 to burn to SVCD. Not DVD.
I've tried all manner of bitrates, and since SVCD max is 2520 I can safely say I've now tried all possibilities. I've also tried 2-Pass with highest quality motion precision. The results are indeed better, but the problem is not fully resolved. So I still find I prefer MPEG1 (which I'm encoding at bitrate 1500), where the motion is is fine, over SVCD. Which is a shame since of course the quality of SVCD is 25% better - or at least it would be if I could solve this motion-pixeling problem.
Does anyone have any other ideas?
Many thanks.

[wulf109]

I really think 2-passVBR is the solution. I encode at 2250 average,3500 maximum,o minimum. I see no pixelizing in the 46 min. SVCD's I make. The maximum you can set in VBR mode is really dependant on you DVD player. I have a Sampo player that happilly except a 9800 maximum bitrate. My Daewoo stumbles at 9800 but will play 8000 without problems.

[Truman]

tobenfun, you did not say which encoder and other tools you use. If you use TMPGEnc, try the soften block noise filter as Tommyknocker said. This "pixel effect" is really caused by low bitrate. Since you want to create a SVCD, the total bitrate limit is 2788 kbps, so a max of 3500 is no solution. If your player accept XSVCD, you may try that, but it is off standard.
A MPEG encoder need a very high bitrate to encode a frame properly, if the source frame is very detailed (noise is also a detail) and if the edges are very sharp. A soften filter to blur the picture a little might help.