Add Subtitle to an Avi in a Black Rectangle with Mencoder

With the command below it is possible to add a subtitle to a movie which allready had a subtitle  embedded. It is impossible to make readable a second subtitle on it without this command.

Not: This works on Linux OS.

mencoder -oac copy -ovc xvid -xvidencopts fixed_quant=3 -sub-bg-alpha 1 -subpos 90 -subcp cp1254 -sub "Akira.Kurosawa.Seven.Samurai.1.sub" -o "a1.avi" "Akira.Kurosawa.Seven.Samurai.1.avi"

-sub-bg-alpha 1 (Draws a black rectangle, 150 draws semi transparant rect.)
-subpos 90 ( 90 is the bottom, 50 is the middle of the screen)
-subcp cp1254 ( For Turkish encoding )