sudo vi /etc/mplayer/mplayer.confsearch for the line with pulse and remove it
it should look like this
I found that vdpau video output option works
mplayer -vo vdpau http://fd.fabiensanglard.net/dEngine/doomRotated.mov
but i didn't notice any lower cpu usage
maybe i need to install vdpau packages for nvidia from ubuntu repository ?
ps: I have founded that link on reddit related to Doom classic code review