Media Framework - GPU Video Decoding possible?

I am working on a 360 video project that requires playback of simultaneous 4k 360 Video in a VR headset. The project is targeted at high-end headsets, not mobile. So this should be feasible with current hardware. Windows based, high end GPU available.

Using H264 in a .mp4 container and playing back multiple clips in Unreal Engine is currently CPU bound, the GPU is not doing any work. Does Unreal support GPU video decoding with any combination of video format and codec?

I have tried the FFMPEG plugin found here, and can see no performance difference;

Any tips appreciated!