[MEncoder-users] MPEG-2: vrc_minrate and vqmin / lmin

I was getting many distracting blocking artifacts in some of the MPEG-2
videos I was encoding that contained detailed gradients and set out to
atleast minimize the problem.

I created a decent RGB radial gradient PNG using Flash; to use as a
testing video.

I was able to determine that if I lowered vqmin and lmin to 1 AND set
vrc_minrate=1 (or anything above 0), I was able to remove the blocking.
I also set dc=10 because if I left the default, the encoded video would
contain small pulsating black blocks. If I don't set vrc_minrate to
higher than 0, the blocks still appear.

Here's an example command line: * Note I blew up the bitrate to ensure
I would have more than enough to spare.

mencoder -sws 9 -oac lavc -ovc lavc -of mpeg -mpegopts
format=mpeg2:muxrate=18080:tsaf -vf/
harddup -srate 48000 -af lavcresample=48000:0:2 -lavcopts /
vcodec=mpeg2video:vrc_buf_size=3835:vrc_minrate=1:vrc_maxrate=18000:vbitrate=14000:trell:mbd=2:/
preme=2:dia=4:predia=4:precmp=2:cmp=2:subcmp=2:cbp:mv0:acodec=ac3:abitrate=224:keyint=12:/
vqmin=1:lmin=1:dc=10:vstrict=0:vpass=1:aspect=16/9 -ofps 24 export.avs
-o banding.mpg

However, if I set the min_rate above 0, I get this message:

[mpeg2video @ 00D85BA0]Warning min_rate > 0 but min_rate != max_rate
isn't recom
mended!

1. Why isn't this recommended?

2. Any ideas why vqmin=1 and lmin=1 don't remove the blocking unless I
include the vrc_minrate >0?? What is actually going on?

3. In the man, it says vqmin=1 is "Not recommended (much larger file,
little quality difference and weird side effects: msmpeg4, h263 will be
very low quality, ratecontrol will be confused resulting in lower
quality and some decoders will not be able to decode it)." What are
these weird side effects? Does MPEG-2 video suffer from these side
effects?? Or DVD compliant MPEG-2 video? In this test, I've only
noticed better quality with vqmin=1 with mpeg2video.

4. In the man, it says that "Lowering lmin will make lavc more likely to
choose lower quantizers for some frames, but not lower than the value of
vqmin." If this is the case, why does the man say that lmin can ==
0.01 when vqmin can't go lower than 1.

5. Are all of the options that are noted with (pass 1/2) in the man
disabled if you include them in the second pass? Or can they be
detrimental if you include them on a second pass?

Your help is appreciated,

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