Media Texture Resolution Limit?

We are looking at creating a GearVR app using a media texture sphere. Our original 360 footage is 4K. I can’t seem to get it or a 2K version working in Unreal as a media texture, but it works with full HD. Is 1920x1080 the media texture size limit? Thanks for the help!

This seems to be answered here:
Media Framework 360 Video?