[MEncoder-users] new doom9 codec comparission

[Corey Hickey]

Here is my semi-final mpeg-4 encoding line for Doom9.

for i in 1:turbo 2 ; do
  mencoder matrix.vob -aid 128 -oac copy \
-vf crop=718:356:0:60,scale=640:272 -sws 9 -ovc lavc \
-lavcopts vcodec=mpeg4:vbitrate=581:mbd=2:mv0:trell:cbp:\
precmp=2:cmp=2:subcmp=2:predia=2:dia=2:preme=2:v4mv:\
last_pred=2:vqcomp=0.6:vmax_b_frames=2:vpass=$i \
-ofps 24000/1001
done

After a couple dozen full encoding tests and numerous partial ones, the
best result I have is little different from the "Very high quality"
suggestion in the mplayer docs. Differences are:

----docs --------mine---------------reason-----------
last_pred=3    last_pred=2   slower, no difference
vb_strategy=1  <default>     lower PSNR, worse quality
qns=2          <default>     too slow for this test

If anybody has anything to suggest or spots anything wrong, please speak
up now. Unless I hear any dissent I'm going to send it to Doom9 tomorrow
evening.


Further notes:

I have been unable to find a suitable value for nr. Between nr=0 and
nr=400 it seems to be a general progression toward loss of detail
without any corresponding reduction in blockiness. Mostly it makes
stubble on men's chins look blurry.

last_pred=1 is a bit better and a bit slower than the default.
last_pred=2 is a bit better and a bit slower than last_pred=1.
last_pred=3 seems the same as last_pred=2 and is slower still.

Unfortunately, the quality drop from using threads=2 is, in my opinion,
unacceptable. The quality is a little bit worse than when not using any
B-frames. Fortunately, encoding speed is still pretty good: the first
pass runs at 92fps and the second at 29fps, yielding an average of
44fps. My computer is about as fast as the one used in the 2004
comparison, and this puts encoding speed at the high end of mid-range
when compared to the codecs in the 2004 encoding tests. I think that's
good enough, especially since quality is still the primary criterion.

The other item of bad news is that I can't get spp to run fast enough on
windows with Media Player Classic. I don't know where the fault lies,
but if it doesn't come even close to working on an AthlonXP 3200+ I
doubt it will be acceptable on whatever machine Doom9 uses. I'll have to
fall back to using ffdshow's "mplayer postprocessing" with "accurate
deblocking".



Coming up: snow

I've been queuing up snow tests to run in the early morning after that
night's mpeg-4 encodes finish. I have a few more that will run tonight.
The snow command will be like the one above, except with these differences:

for i in 1:vqscale=2.15 2:vbitrate=581 ; do
  ...same options as above...
  -lavcopts vcodec=snow:vstrict=-2:cmp=1:subcmp=1:mbcmp=1:qpel:vpass=$i
done

Some time tonight my computer will test the effect of threads=2 with and
without last_pred=2.

-Corey