Get CCC full package (that make sure you also get the AMD media codec) and install the CCC (check AMD media codec is installed correctly in installation log which pops up after installation). Download Media Player Classic. Install and enable GPU DXVA in MPC by:
Enable DXVA (includes all .264 content regardless if it is mkv, mp4, etc...) in MPC by going:
View>options>internal filters and select everything with (DXVA) and apply
Then, on playback>output select
evr custom pres, directx9 and directx9, for directshow video, realmedia video and quicktime video
Ok and restart MPC and play video.