Optical flow
Also known as: motion estimation, optical flow retiming
A technique that analyzes how pixels move between frames, used to create new in-between frames for smooth slow motion or to stabilize and stitch footage.
Updated
What it means
Optical flow estimates the motion of every part of an image from one frame to the next. Once the software knows where each pixel is moving, it can generate new frames in between that never existed in the original footage. That makes smooth slow motion possible from clips recorded at normal frame rates.
Editors use optical flow for retiming in time remapping and speed ramps, 360 software uses similar analysis for cleaner stitching, and some stabilizers use it to understand camera motion.
Newer AI-based tools take the same idea further, as covered under frame interpolation and AI slow motion.
How it works in practice
In your editor, choose optical flow as the frame blending method when slowing a clip beyond what its frame rate allows. Preview the result carefully, since quality varies with content, and compare it with simple frame blending to see which looks better for each clip.
It works best with simple, predictable motion: a car on a road, a slow pan across a landscape, water flowing steadily. It struggles with complex overlapping motion like spokes, splashes, crowds and limbs crossing each other.
When possible, record at a high frame rate instead and use optical flow only to stretch a little further.
What to watch out for
The typical artifacts are warping, smearing and ghostly edges where objects overlap, such as a hand passing in front of a face. These can be very visible in action sports, where limbs, boards and spray constantly overlap.
Processing is slow, especially at high resolution. Render optical flow sections before judging them, since real-time previews may not show the final quality. Rendering only the short retimed section saves a lot of waiting.
Optical flow cannot invent detail that was never captured. Motion blur in the source frames remains, and generated frames may look softer than real ones, which matters most in slow replays.
How RawClip handles it
RawClip uses your clips at their recorded frame rates and focuses on picking and cutting the best moments. Record slow-motion moments at 60 to 120 fps for the smoothest result in your highlight.