VAAPI

VAAPI (Video Acceleration API) provides access to graphics hardware (GPU) acceleration for video processing.

Global
VAAPI support can be enabled system-wide by adding the  value to the USE variable:

Enabling VAAPI support will pull in the package, which has the following USE flags:

These flags can be adjusted in.

The system needs to be updated if the USE variable has been set to :

Usage
Emerge and run  to check VAAPI support.

It is possible to override the automatic VAAPI driver selection with the  variable:

 Intel: For libva-intel-driver use i965. For libva-intel-media-driver use iHD. 

NVIDIA: For Nouveau use nouveau. For NVIDIA use vdpau. </li>

ATI/AMD: For AMDGPU driver use radeonsi.</li> For AMD Catalyst use fglrx.</li> </ul></li> </ul>

When setting  to a driver for a secondary GPU, be sure to set   accordingly as well.

VLC
VLC supports VAAPI natively. Activate the appropriate setting through the preferences menu.

mpv
mpv also supports the VAAPI acceleration through the command-line option.