[MEncoder-users] Output bitrate significantly less than vbitrate

[n0dalus]

Hi,

I am trying to produce valid mpeg2 video for use in dvd players.
The problem is that I keep ending up with undersized video.

I am trying to encode 22 minutes of PAL ogg video into a 700mb mpeg2.

mencoder -of mpeg -vf scale=720:576,harddup -oac lavc -ovc lavc
-lavcopts acodec=ac3:abitrate=192:vcodec=mpeg2video:keyint=25:vbitrate=4251648:aspect=4/3:vrc_maxrate=9800:vrc_buf_size=1835:vpass=1
-mpegopts format=dvd -srate 48000 -passlogfile 'video.pass' -o
'video.mpg' 'video.ogm'

For the second pass I just change it to pass=2 (I assume it doesn't
hurt to leave the other options there.)

The vbitrate of 4152kbps (k = 1024) combined with a 192kbit abitrate
should produce a total average bitrate of 4344kbps. For 22 minutes of
video this should produce a 700mb file. However I get a ~400mb file. I
thought I would tell it to use a higher bitrate (like 9000kbps) to
test it and hope that it would average out higher, but it was only
just more than 400mb.

I have read that this has to do with vqmin/vqmax/lmax/lmin and
vqscale/vqcomp but I have no idea which, if any, of those I should try
to change. Searching the list archives, I was able to find a few
references to a similar problem, but with several conflicting ideas
(some say don't touch vqscale, some say changing vqscale will reduce
video quality in high motion scenes, some say don't use vbitrate at
all but instead use vqscale, etc.) I am also concerned that changing
these values might create something that isn't playable on dvd
players.

In essence, how do I get mencoder to produce dvd-complient mpeg2 video
with an average bitrate equal to my vbitrate setting. I am needing to
automate this for an unknown number of files (I have a script that
produces the mencoder command from values it parses from a test run of
mplayer), so I would rather not have to do too much trial and error (I
can program the script to automatically adjust certain values given
the output file size and try again, but I would rather it got it right
1st try.)

n0dalus.