Free filtering using custom quants?

trbarry · 12th February 2003, 00:58

When you have a noisy source or are going to encode at a very low bit rate sometimes it's better to filter the heck out of it first, removing high frequency components that will cause artifacts and be hard to compress.

It's come up a couple times here before that it might be possible to just use Xvid custom quant matrices to sort of do this for free, with no run time CPU cost. I asked about it a couple times last summer but it seemed custom quants were busted then.

But since then they've apparently been fixed and this morning I played with it for awhile.

For an extreme case I made quant matrices that had the value 99 in most all but the top left few positions (see attached file SoftMatrix.zip). Then I made a 1280x720p 1 pass CBR of the recent HDTV Daredevil trailer at only 2.5 mbps, usually too low for most HDTV. It actually came out pretty good, better than I had expected.

Can anyone tell me what max number I'm allowed to use in Xvid custom quant matrices? I just filled in 99 and it seemed to work but I don't see it documented anywhere. I want a number that just forces some DCT components to zero as much as possible.

- Tom

12th February 2003, 00:58	#1 \| Link
trbarry Registered User Join Date: Oct 2001 Location: Gainesville FL USA Posts: 2,092	Free filtering using custom quants? When you have a noisy source or are going to encode at a very low bit rate sometimes it's better to filter the heck out of it first, removing high frequency components that will cause artifacts and be hard to compress. It's come up a couple times here before that it might be possible to just use Xvid custom quant matrices to sort of do this for free, with no run time CPU cost. I asked about it a couple times last summer but it seemed custom quants were busted then. But since then they've apparently been fixed and this morning I played with it for awhile. For an extreme case I made quant matrices that had the value 99 in most all but the top left few positions (see attached file SoftMatrix.zip). Then I made a 1280x720p 1 pass CBR of the recent HDTV Daredevil trailer at only 2.5 mbps, usually too low for most HDTV. It actually came out pretty good, better than I had expected. Can anyone tell me what max number I'm allowed to use in Xvid custom quant matrices? I just filled in 99 and it seemed to work but I don't see it documented anywhere. I want a number that just forces some DCT components to zero as much as possible. - Tom Last edited by trbarry; 12th February 2003 at 01:01.