You can use Gnome Mplayer to have hardware acceleration
1. Gnome Mplayer > settings > player > use vaapi on videooutput
2. Gnome Mplayer > settings > Mplayer > give additional parameter: -vo vaapi -va vaapi
After that CPU load will decrease! On my Notebook CPU load shrinks from 40% to 16%
I was also not able to use vaapi with SMPlayer and I created a bugreport about that.
My preffered Player is VLC and it is also not using hardware acceleration although there is just a small trick to do during building. I also created a bugreport for VLC and vaapi.
Hope to see soon some improvement regarding SMPlayer and VLC