[MEncoder-users] how to decide the place of "harddup" video filter in the video filtler chain?

[littlebat]

Hi,

I am using mencoder to converting some videos. I read the man page about
"harddup" video filter, it is said "Should be placed at or near the
end  of  the filter chain unless you have a good reason to do
otherwise.". But, I found it must be placed before the "aspect" filter
or must be placed at the begin of the video filter chain sometimes.
Anyone can tell me the guideline of how to decide the place of "harddup"
video filter in the video filtler chain?

There are two examples about can't place "harddup" at the end of
the filter chain:
1. When the destination aspect is greater than orginal aspect, I need
add black bar at the left and right side of the orginal video first, if
I miss the "harddup" or place it at the end of the video filter chain,
the destination video will has double width black bar at the right side
and has no black bar at the left side. Here is my command line can get
the right result: 
mencoder -noconfig all -ovc lavc -oac pcm \
-lavcopts vcodec=mpeg4:vbitrate=384 \
-vf expand=385:289,harddup,scale=320:240 \
-af volnorm -of lavf -ofps 15 -lavfopts format=mkv \
-o /tmp/tmp.wGbbJEoGEb.mkv  /home/mdx/AVSEQ11.DAT -ss 0 -endpos 228

The original video is a vcd file, it has 352x288 resolution, you can
download a 2M sample slice "test1.dat" at:
http://www.learndiary.com/upload/test1.dat

2. The original video is still a 352x288 vcd file, if I use the same
command line as above, I get the error report such as below:
<qoute>
1 duplicate frame(s)!
    Last message repeated 122 timesTrem:   0min   0mb  A-V:-0.019
[0:1411] Error while decoding frame!
</quote>
If I move the "harddup" to the begin of video filter, it works
normally. The working video filter is 
"-vf harddup,expand=385:289,scale=320:240"

You can download a 2M sample slice "test2.dat" at:
http://www.learndiary.com/upload/test2.dat

Thanks.

littlebat