I honestly have no idea, as I've never worked with Unreal's velocity buffer implementation. We simply push a triangle soup to the renderer by sub-classing ProceduralMeshComponent. I can't even find any good documentation on UE's velocity buffer impl. Can you point me in the right direction? From what I can gather from dispersed UE forum posts, it appears to be some setting on the materials, not so much something the renderer itself needs to do.