>This makes me wonder: There is a difference
>between a clean, high quality stream from a human
>perspective and from the perspective of an
>encoder (in the sense that is is 'easy' to
>encode), is there? If there is no difference,
>then there is no point in talking about video
>processing that improves video streams
>numerically (for encoding), but not visibly.
Yes, there's a difference. A human may not be
able to tell the difference between luminosity
levels 128 and 129, but the computer can, and if
you have a screen that's all 128-level except for
lots of 129-level dots spread throughout randomly,
the computer is going to waste a lot of space
encoding it, and if the pattern of 129-level dots
changes every frame, motion-detection will fail
too. But it'll all look the same to a human
being. From this simple example, one can easily
infer that something that looks the same to a
human being does not necessarily look the same to
the computer.
>Many users lack the knowledge to process their
>video material in a way that allows mpeg2enc to
>get the most out of it.
Us developers too :-)
I've been working on how to convert the analog
sources in my collection (LaserDiscs and VHS
tapes) to very clean VCDs/DVDs. It's taken 2 1/2
years. I've had to write a new denoiser, I had to
beg other programmers to make fixes in parts of
the code, and slowly I'm getting to my goal.
>I'm working on a bash script (and a Wizard style
>Kommander GUI to control it) for using mpeg2enc,
>which features 'source profiles' like 'consumer
>DV camera', 'Computer Generated' or 'VHS Tape'.
My scripts, and the ones you're generating, should
end up as part of mjpegtools, part of some future
GUI video-editing system, and as notes in our
HOWTO.
>If there are general processing methods that are
>beneficial for *any* video stream that needs to
>be reduced to MPEG, it is desireable to perform
>such processing by default.
In many cases, the default values strike a balance
between quality and speed. For instance, there's
no need to make the user pay for "mpeg2enc -4 1 -2
1" until they're ready for it and willing to pay
the price.
>Perhaps a section in the mpeg2enc manpage about
>stream conditioning would help.
Sure...as soon as we know how to do it :-)
>>I'm not quite sure though what is meant by
>"numerical conditioning".
>
>Any processing that has no visible effect, only
>numerical.
y4mdenoise run at very low tolerances ("-z 1 -t 1"
or "-z 1 -t 2") qualifies as such processing.
Steven Boswell
ulatekh at yahoo dot com
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