[XviD-devel] HUGE ME regressions between beta1 and beta2

[Michael Militzer]

Hi Radek,

well, I've basically just changed our lambda tables. Before, the values for
lambda were borrowed from h.264 it seemed however didn't fit XviD's linear
qscale at all. In result, R-D performance especially for higher QPs was
absolutely horrible. I've changed it to a more lambda = 0.85*Q scheme (ok,
can't recall the exact constant from memory now). I've tested the change
for VHQ and non-VHQ modes and had always superior performance, sometimes 
with really huge gains especially a low bit-rates/high quants. 

I've attached my original mail to the list at the end of this mails and also
reposted some of the R-D curves I did at those times. Your testing case is
covered as well (it seems).

Sure we can postpone 1.1 final until this problem is fixed. BTW: did you use
a standard sequence for your test so we can reproduce the problem?

Regards,
Michael


Quoting Radek Czyz <radoslaw at syskin.cjb.net>:

> Hi everyone,
> 
> Apparently our testing community sucks ;))
> 
> There was a HUGE quality and speed regression between beta1 and beta2. I 
> narrowed it down to SAD-based ME. The major changes in that time was 
> Isibaar's new lambda code, but apparently we have hardly any logs what 
> happened exactly (well, we've got cvs, I'll check that).
> 
> For fast settings (no VHQ, no trellis, no chromaME, defaults otherwise):
> 
> Beta1's ME:  time 1:19 filesize 26.2MB psnr 41.19dB
> Current ME:  time 1:24 filesize 28.8MB psnr 41.14dB
> 
> 
> What the heck happened? ;_;
> 
> I suggest we postpone 1.1final until we figure this out - looks like all 
> speed improvements over 1.0 are gone (10% slower at these settings, 5% 
> slower at defaults), and 10% more filesize for *lower* quality is... bad.
> 
> Radek
> _______________________________________________
> XviD-devel mailing list
> XviD-devel at xvid.org
> http://list.xvid.org/mailman/listinfo/xvid-devel
> 


----- Forwarded message from Michael Militzer <michael at xvid.org> -----
    Date: Mon, 14 Mar 2005 19:59:37 +0100
    From: Michael Militzer <michael at xvid.org>
Reply-To: Michael Militzer <michael at xvid.org>
 Subject: low-bitrate patch
      To: xvid-devel at xvid.org

Hi all,

I've committed a patch to cvs that improves XVID's performance at low-
bitrates by using better lambda values for R-D vector search. By this also
mode decision (SAD-based) is improved at low-bitrates. At mid/higher bitrates
there's no change in performance, so only people who aim at really low
bitrate (and quality) encodes will benefit from this patch.

I've attached some R-D graphs that compare the behavior of patched and 
unpatched XVID for various sequences and different bit-rates. Note that I've
used a logarithmic scale, so that the differences at low bitrates can be
better perceived. As can be clearly noticed, the compression performance is
enhanced significantly at very low bitrates (up to 2-3 dB PSNR).

Well, it's another question how useful this patch actually is because such
extremely low bit-rates are barely used. But for completeness, XVID should
perform equally great at all bitrates...

bye,
Michael

----- End forwarded message -----