The BCC Optical Flow ﬁlter estimates the motion between two frames of video and renders an intermediate frame that interpolates the motion. The synthesized frame contains a mixture of the previous and next frames, each distorted by an amount determined by the optical ﬂow estimation. With this ﬁlter, you can smoothly slow down or speed footage. Optical Flow generally produces smoother animations than a velocity remap ﬁlter.
Optical Flow synthesizes frames needed to complete the effect instead of blending adjacent frames as most retiming applications do. In essence, Optical Flow manufactures entire frames. Optical Flow analyzes the frames before and after the current frame to determine which pixels are moving. Then, only the moving pixels are synthesized, repositioned and composited into the new frame. The intervening information is created by warping the two frames, estimating where each individual pixel should be at every new in-between point.