After many research, i have found an alternative solution for "auto kill" zombie of MEncoder.
I use ps-watcher (http://ps-watcher.sourceforge.net/
), it'a a perl script running as daemon.
Here my config file:
trigger = elapsed2secs('$etime') > 6*HOURS
occurs = every
action = kill -9 $pid
ps-watcher run every 10min, and search if a process mencoder run since 6 hours...
Basic, dirty, but run...
Intel Core 2 Duo E6600 - 4Gb Ram - Debian Lenny NetInst with Multimedia source list - jre1.6.0_24