and here a PDF with more info... https://cdn2.unrealengine.com/Unreal+Engine%2FWhy-Real-Time-Technology-is-the-Future-of-Film-and-Television-Production-ecc14547ab8a340d4c00e2f931adfcf3a201478d.pdf
A cinematic character may have a very advanced rig with lattice\cage deformers, plus custom drivers\set-driven-keys with complex expressions, things that the game engine isn't likely to support (beyond the standard skinning and morphing). So one thing that people have done to be able to use a real-time renderer for this…