[MEncoder-users] new doom9 codec comparission

Corey Hickey bugfood-ml at fatooh.org
Tue Dec 6 08:29:56 CET 2005

I've been quiet for the past couple days because it took a while to get
some conclusive results in the time I had. My work is paying off,
however, and I should be able to submit a set of very refined mpeg-4
lavcopts for your review some time tomorrow. I have a few tests left to
run overnight.

Some interesting notes:

Adding b-frames does indeed increase PSNR on this movie.
vmax_b_frames=0:   PSNR: Y:41.31, Cb:44.26, Cr:44.73, All:42.13
vmax_b_frames=1:   PSNR: Y:41.72, Cb:44.83, Cr:45.42, All:42.58
vmax_b_frames=2:   PSNR: Y:41.78, Cb:44.93, Cr:45.57, All:42.66
vmax_b_frames=3:   PSNR: Y:41.71, Cb:44.99, Cr:45.65, All:42.61

I stuck with vmax_b_frames=2. Using vb_strategy=1 on the first pass
always decreased final PSNR slightly; quality was slightly lower as well.

Thanks go to Jan Knutar for pointing out a potential pitfall -- there
was indeed some flickering produced by using spp=2 to play the videos
with b-frames. When I looked closely, the flickering was still there
without spp, just less visible. Removing the quantizer difference
between p- and b-frames makes the flicker go away entirely, at a cost of
decreased PSNR and a visible quality loss. I've settled on
vb_qfactor=1.1:vb_qoffset=0.6 as a reasonable compromise. This lowers
the overall PSNR to 42.53, which is still a substantial gain over not
using b-frames, while reducing the flicker to the point at which it is
hardly perceptible.

I tested all the various *_mask options along with naq, but was unable
to find any reasonable levels. At extreme parameter values, the raised
quantizer was visible where it was supposed to be for each corresponding
option, but I couldn't see any substantial gain in the rest of the
video. At more moderate values, the visual quality ranged from identical
to slightly less than that of the original. Also, for what it's worth,
each test lowered PSNR slightly.

Unless anybody has any specific favorite values they'd like me to test,
I'm going to forget about *_mask.

If you noticed the email I cc'd to the list earlier today, you'll see
that I'm having problems tuning spp appropriately with ffdshow. I may
have to settle for more traditional postprocessing. In ffdshow, enabling
the "mplayer" processing method and "Accurate deblocking" looks more or
less ok, but not as good as spp=2.


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