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.