On Wed, 17 Sep 2003, Richard Ellis wrote:
> Thanks for the pointer, yes, I looked at the diffs and the code that
Welcome.
> is driven by Q (in that section at least) was reworked quite a bit in
> January. That would account for the difference I'm seeing in the new
> mpeg2enc's Q that does not seem to be having much effect at times.
At least not with the default value of -X (100). I think
experimenting with -X could make -Q have more effect.
> > Ideally -X should be documented of course ;)
>
> Actually, if no one else wants to, I can do some documentation
> patching and submit a diff to the list of the changes. Of course,
I'll put it on the TODO pile - a sentence or two in the manpage
won't be too difficult.
-X is, I believe, mentioned in the usage() summary - so if nothing
else a person can run "mpeg2enc -h" and see it mentioned there.
> The differ only after 413,364,142 bytes (about 1/2 of the way into
> the files). So it appears that, the new -Q had zero effect for that
> pair of encode runs. The total file sizes differ by only 4 bytes.
I believe that qualifies as statistically insignificant :)
> > Perhaps -N <num> (num =0.0 to 2.0) would work as well. In 1.6.1
> That is a good suggestion, thanks. The new adjustable -N value
> should be able to accomplish much the same level of "fine tuning"
That's what I've been using it for. The higher the value the
smaller the file (because the high frequency quantizers are
raised - high -N values will lose detail). -N 0.5 is very
mild, 1.0 I've found to be a good middle point for preserving
detail but still saving bits.
The other thing that can be used to regulate the size is the
-K option and use of the alternate quantizing matrices. So far
I've settled on '-K kvcd' as producing very good pictures (the
dark scenes look better than before) but perhaps the tmpegenc
tables might, on some material look better.
Have fun experimenting!
Steven Schultz
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