[MEncoder-users] Encoding test results

[Grozdan]

2009/8/3 Matyas <mplayer.list at sustik.com>:
> A ran some x264/mencoder encoding tests in order to find out whether single
> or two pass encoding is best suited for my needs.
>
> I used log=3 and then plotted the SSIM values from octave, the results are at:
>
> sustik.com/mencoder-tests/.
>
> Below are some explanations regarding what exactly I did.  I plan to run
> further tests using other type of sources and parameters.  Suggestions and
> comments regarding the tests and the results are welcome.
>
> The source is a 24fps (progressive) movie containing 140629 frames, which was
> cropped to 656 x 448 size.  I also used the hqdn3d=2:1:2 filter in all runs.
>
> The x264 options:
> X264OPTS=pass=1:subq=7:8x8dct:frameref=4:bframes=9:b_adapt=1:weight_b:\
> b_pyramid:nointerlaced:nofast_pskip:trellis=1:mixed_refs:weight_b:me=umh:\
> me_range=32:nodct_decimate:partitions=all:psy-rd=0.5,0.3:qcomp=0.7:\
> direct_pred=auto:keyint=300:threads=auto:psnr:ssim:log=3

Both psy-rd and AQ lower PSNR and SSIM but increase quality. Thus you
should not trust that much these metricses as was explained many times
by Jason (x264 dev). You should do all your tests with psy-rd (and
maybe AQ) disabled. Also no one uses qp for real encodes as there is a
much better and intelligent option in the form of crf.


>
> (The second pass used the same options; some runs with turbo=2 added, and
> crf, qp, bitrate set as applicable.)
>
> I used:
> MEncoder SVN-r29443-4.3.2
> x264 - core 68 r1189 9d0b5e9
>
> I compared three single pass encodes first.  crf=23 resulted in a 656 kb/s
> file, qp=23 produced a 626 kb/s file.  So I also ran a single pass with
> bitrate=656.
>
>        crf=23       qp=23         bitrate=656
> PSNR    43.683       44.519        43.588
> SSIM     0.9784801    0.9794548     0.9782447
> kb/s   656.35       626.86        656.84
>
> The SSIM graph (per frame) for qp=23 and bitrate=656:
> qp=23.bitrate=656.compare.png
> (On the graphs in parenthesis: the mean SSIM and standard deviation.)
> For crf=23 and bitrate=656:
> crf=23.bitrate=656.compare.png
>
> Next, I ran a two pass encode using a qp=23 first pass and 626 kb/s second pass:
> qp=23.compare-passes.png
> I did not expect the second pass do worse but that appears to be the case
> (for this source anyway):
>
>       "qp=23 1-pass"      "qp=23 1st pass, bitrate=626 2nd pass"
> PSNR    44.519              43.793
> SSIM     0.9794548           0.9787170
> kb/s   626.86              626.17
>
> Then I ran a 2-pass encoding with both passes using bitrate=656, the first
> pass used turbo (this is how I encode usually).
>
> qp=23.2-pass-turbo-bitrate=656.compare.png
> Compares the results (compared to qp=23 since it was better than crf=23).
> The qp=23 single pass produced the best result, even the standard deviation
> was better.  I also run the 2-pass encoding without turbo.  That did not
> improve the results, in fact it was worse (which I did not expect).
>
> I did other runs like a 2-pass with a crf=23 as first pass, that was slightly
> better than the one-pass crf=23, but worse than the one-pass qp=23.
> (I tried a 3-pass encoding to see what happens; a segfault happened in the
> second pass...)
>
> Matyas
> -
> Every hardware eventually breaks.  Every software eventually works.
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