 The "large" context model uses (11*11*5*5*5+1)/2=7563 contexts based on the same values as before, but also (TopTop - Top) and (LeftLeft-Left), where "TopTop" is the pixel two above the current one vertically, and "LeftLeft" is the pixel two to the left of the current one.In arithmetic coding, each "context" actually has 32 sub-contexts used for various portions of coding each residual, resulting in a grand total of 242,016 contexts for the "large" model.The arithmetic coder of FFV1 is very similar to (and based on) that of H.264.