[MPlayer-users] mencoder: Removing black bars creates black line artifacts

[Trevor Bradley]

Hey everyone.  I love mencoder.. It's great for batching up mpgs I've 
recorded with MythTV to convert to AVI.

I've figured out how to remove the black bars at the top and bottom of 
widescreen programming.  Presently I'm using the following commands to 
transcode files:

mencoder filename.mpg -quiet  -vf lavcdeint -vf crop=704:352 -ovc xvid 
-oac mp3lame -xvidencopts pass=1 -o /dev/null
mencoder filename.mpg -quiet  -vf lavcdeint -vf crop=704:352 -ovc xvid 
-oac mp3lame -xvidencopts pass=2:bitrate=1300 -o filename.avi

And this works well, producing an avi file with the black bars removed.

However, the quality of that avi is different than if I don't crop the 
file.  When the scene pans with a fast horizontal motion, I see black 
horizontal lines, perhaps 1-2 pixels tall across parts of the image that 
don't appear if I transcode to avi without the cropping.   It's subtle, 
but bad enough that I've thrown out the avi rather than the larger mpg file.

Here's a sample of the file uncropped, and the same frame (or very close 
one) uncropped:

Uncropped, Clean: http://www.internetgenealogy.com/mencoder/snapshot1.png
Cropped, with evil lines: 
http://www.internetgenealogy.com/mencoder/snapshot2.png

Note how some objects, like the brims of the soldier's hats, have 
striking horizontal lines in the second snapshot.  It's not in every 
frame, but it's annoying.  In other scenes, like those with quickly 
moving shadows (like peoples faces and the shadows cast by their noses) 
the effect is quite striking.

(This is from the new Ken Burns PBS series "The War" if you're curious).

mencoder -v reports:

MEncoder 1.0rc1-3.4.6 (C) 2000-2006 MPlayer Team
CPU: AMD Athlon(tm) 64 Processor 3500+ (Family: 15, Model: 79, Stepping: 2)
SSE2 supported but disabled
CPUflags: Type: 15 MMX: 1 MMX2: 1 3DNow: 1 3DNow2: 1 SSE: 1 SSE2: 0
Compiled for x86 CPU with extensions: MMX MMX2 3DNow 3DNowEx SSE

Am I perhaps running the crop command incorrectly?   Is there a better 
tool for stripping the black bars out of the MPG before I attempt to 
transcode?

Thanks for your help!  Any advice would be appreciated.

Trevor Bradley
Surrey, BC, Canada