This could be useful for users not running the most powerful computers. Checked the average CPU usage whilst playing the same .mkv file in 480P resolution. Using
Stretch 7.5 (which by the way uses the least cpu overhead of any operating systems I've tried):
mplayer no GUI - Uses the least CPU power so let's take it as the base to work from.
gnome-mplayer (basically mplayer with GUI) - 20% more than mplayer
mpv - 50% more (I'm surprised at this).
VLC - about the same as gnome-player at about 20% more (I thought it would be more).
Interesting...