I wanted to letterbox one of my anime episodes (Bleach - Episode 24) but kept getting an error in vdubmod:

Error decompressing video frame 0:

A codec specific error has occured.
(error code 1)
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I got some of the episodes before episode 24 to resize to letterbox in vdub. But now I can get anywhere in vdubmod. I have 3gp converter and it re-encodes it nicely (re-encode = bad, I know), but it will not resize to letterbox like I want it to. This is the coding for my encode:

Command0=""<%AppPath%>\cores\ffmpeg" -y -i "<%InputFile%>" -timestamp "<%TimeStamp%>" -bitexact -vol 500 -vcodec xvid -fixaspect -s 640x400 -r 29.97 -padtop 40 -padbottom 40 -b 800 -acodec mp3 -ac 2 -ar 44100 -ab 128 -f avi "<%OutputFile%>.avi""
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Whenever I do the padbottom and padtop, the left and right side also resize. Anyone got any suggestion on what to do? I tried the "letterbox" command for my avs scripts too but no luck. I'm watching this on TV so I want them black borders ONLY on the top and bottom.