FUSION · NODE REFERENCE
OpticalFlow
Motion-vector analysis between frames
OpticalFlow estimates motion between neighboring frames and adds Vector and Back Vector channels to the image. Downstream tools such as TimeStretcher use this data; the node itself does not slow the clip or create a visible blur effect.
OpticalFlow
Overview
What OpticalFlow does
OpticalFlow analyzes temporal changes in the image. One Input receives the frames; separate Vector and Back Vector sockets are unnecessary because the data travels inside the image as AUX channels. Connecting Output directly to MediaOut will normally look like the original RGB clip: another tool must use the motion calculation.
The Resolve 21 manual distinguishes CPU-based Classic from GPU-based Advanced. Classic preserves compatibility with the earlier method; Advanced exposes the Warp Count, Iteration Count, Smoothness and Half Resolution controls shown in the archive. Larger Warp Count and Iteration Count increase computation, but do not guarantee improvement once the solution converges. Compare contours and actual calculation time on your shot.
Smoothness controls the spatial smoothness of the motion field. Too little can retain noisy vectors; too much can lose distinct motion around fine detail or object boundaries. Half Resolution lowers the analysis resolution; it is not a command to halve output frame dimensions.
Output Vectors as Layers changes how the calculated fields are represented: discrete layers support a compatible multilayer path in addition to conventional AUX workflows. The checkbox is not required for OpticalFlow calculation. The consumer must read the representation being supplied; SmoothMotion has Use Layers for Input Vectors for a layer-based input.
For retiming, connect OpticalFlow to TimeStretcher, choose Interpolate Mode=Flow and animate Source Time. Two linear keys define the required speed; the initial single Source Time key can leave a freeze frame. TimeStretcher uses and removes incoming Vector/BackVector, so generate them again for another motion calculation after retiming.
A cut, flash, heavy blur, repeating texture or occlusion makes correspondence harder to estimate. Analyze a continuous shot with enough neighboring frames. Viewer → Vectors helps inspect the field; Normalize Color Range changes the display rather than the computed data. An intermediate cache needs a format and channel configuration that preserves Vector and Back Vector, such as properly configured OpenEXR.
When to use it
Preparing motion for TimeStretcher Flow interpolation.
Comparing CPU and GPU methods on a difficult shot.
Inspecting and diagnosing motion fields.
Preparing vector layers for compatible tools.
Caching verified fields in a multichannel intermediate file.
OpticalFlow in context
Screenshots referenced by this article. Open an image to inspect it at full size.
Example for OpticalFlow.
Original image