I hope that SMPlayer keeps display off if a video / music is changed.
I have a All-in-one Windows7 desktop PC.
I sometimes use SMPlayer to listen to music by using a playlist.
Display is not needed while playing music.
So I turn display off by using a free soft after a playlist is started.
But when a music is changed , display is turned on by SMPlayer.
SO I hope that you add a new option that SMPlayer doesn't turn display on.