mkfifo video.pipe
mkfifo audio.pipe
mkfifo audio2.pipe

mkvmerge -o 66.mkv video.pipe audio2.pipe &
mencoder 66.mpg -nosound -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=1500:mpeg_quant:autoaspect -o video.pipe & 
oggenc -b 160 -o audio2.pipe audio.pipe & 
mplayer -vc null -vo null -ao pcm:fast:file=audio.pipe 66.mpg &
wait


# Or if mkvmerge won't take pipes, use these

mencoder 66.mpg -nosound -ovc lavc -lavcopts vcodec=mpeg4:vbitrate=1500:mpeg_quant:autoaspect -o tempvideo.avi & 
oggenc -b 160 -o tempaudio.ogg audio.pipe & 
mplayer -vc null -vo null -ao pcm:fast:file=audio.pipe 66.mpg &
wait

mkvmerge -o 66.mkv tempvideo.avi tempaudio.ogg