On Thu, 6 Apr 2006, Christian Ebert wrote:
> >> 1 -V 1853 -s -D 1 0 -g 6 -G 15 -I 1 -b 9800 -D 10 -f 8 -o $1
>
> Does -g 3 make sense in case one has high motion scenes?
Probably not a big difference. The lower limit is mainly used by
mpeg2enc's dynamic GOP sizing logic. If 60% or more of a P frame's
macroblocks are I(ntra) encoded *and* the current GOP size is greater
than the value of '-g' THEN a new GOP is started. Reducing the
minimum GOP size may add a *few* more 'scene breaks' but overall I
doubt it'll make much difference.
> > Also, a search radius of 32 is past the point of diminishing returns...
>
> After a lot of testing it seemed to me that 32 made a tiny
> difference in high motion scenes. But it might be just that I
> *wished* to see a difference -- which tends to be the case after
If it's that kind of difference it probably isn't worth the extra
encoding time :)
> looking at scene for the umptieth time. Is there any other (not
> too complicated) way to test this that does not rely on the human eye alone?
I have seen attempts at that with ffmpeg and the 'psnr' tests - the
compressed video is decoded and compared to the original images and
a signal/noise statistic ('psnr') is computed. The higher the psnr
the closer the encoding remained to the original.
In general the defaults in mpeg2enc are well chosen (the result of
years of use). Overriding them or adding new options, without knowing
what they do, in a "quest for quality" can end up producing surprises
(unexpected and less than desireable results).
Cheers,
Steven Schultz
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