[MEncoder-users] Pulsing Pixelation (?I Frames) in MPEG2 output

[iFrame problems]

I've recently had a lot of trouble transcoding to mpeg2 with mencoder
(SVN-r29092-4.2.4 on Kubuntu/Hardy).

Parameters that produce the problem for me are:
*mencoder -endpos 5 -of mpeg -mpegopts format=dvd:tsaf -vf
scale=640:,expand=720:576,harddup -ovc lavc -lavcopts
vcodec=mpeg2video:keyint=15:vbitrate=1000:vrc_maxrate=7500:vrc_buf_size=1835:
nr=400:trell=yes:mbd=2:mv0:predia=2:dia=2:preme=2:precmp=2:subcmp=2:cmp=2:vstrict=0:aspect=4/3
-oac copy -o output.mpg input.avi*

The output had pulses of blocky pixelation which seemed to occur on I Frames
(same frame frequency as keyint=) and then rapidly corrected over one or two
frames. This was most evident on spacially complex scenes (eg winter forest)
or static pics with sharp edges (logos). It also seems to mainly occur on
bigger source files (>175mb), even if only a small amount (5sec) is
transcoded.

After considerable time spent trying to adjust the bitrate, number of
passes, motion detection and other settings, I finally removed the lavc
option nr=400 with immediate resolution of the problem (all other settings
reverted to original format OK).

I'm not sure if this is a known issue, but thought I'd mention it to
possibly save others some time.