Is it possible to watch a dvb transmission with mplayer and to record it with mencoder at the same time?

Hello,
   is there any way to watch one dvb channel with "mplayer dvb://chName" and
to start and stop recording when needed with a command like "mencoder -o
outfile.avi .... dvb://chName"? I have tried but have had no success. Is
there a way to achieve this simultaneous recording? Maybe even with other
programs or combination of utilities?
The fact is that you cannot know when to stop your recording unless you are
also watching the channel.

Thanx
-- 
Amos Tibaldi
amos dot tibaldi at gmail dot com