In order to use MPlayer for playing video with LPlay, you need to apply patch to MPlayer. Get and extract MPlayer sources (http://www.mplayerhq.hu). Then apply patch from this directory:
cd <directory_of_mplayer_sources>
patch -p1 < mplayer1.0rc1-lplay-v1.patch
If no errors follows, configure MPlayer and add atleast --enable-lplay to configure options:
./configure --enable-lplay
After this, make and make install MPlayer. Now it should be usable by LPlay. You can check, whether LPlay needed video outputs have been compiled: Execute MPlayer executable with option -vo help:
mplayer -vo help
MPlayer should now print out list of supported output modules. You should find datagram and shm from the list.