Concept · Video AI
Frame Interpolation vs Optical Flow
Optical flow is the measurement; frame interpolation is the application. One says where pixels moved, the other uses that movement to draw frames that were never captured. Understanding the link explains why interpolation artifacts happen.
The relationship in one line
Optical flow computes a motion vector for every pixel between two frames ('this pixel moved 12px right'). Frame interpolation then positions each pixel at the intermediate location to synthesize a new frame exactly halfway in time. Flow is the engine; interpolation is the ride.
How each works
| Optical flow | Frame interpolation | |
|---|---|---|
| Output | Motion vectors (per-pixel displacement) | New frames (images) |
| Input | Two frames | Two (or more) frames + flow or learned motion |
| Use | Video stabilization, object tracking, depth | Slow-motion, 24→60fps, HFR delivery |
| Failure | Occlusion, fast motion, textureless regions | Ghosting, warping where flow fails |
| Models | RAFT, PWC-Net, Farneback (classic) | RIFE, FILM, DAIN — often flow-guided |
Why modern interpolators don't use raw flow
Classic interpolation computed flow, then warped. Modern models (RIFE, FILM) learn motion implicitly inside a neural network, using flow-like internal representations plus refinement passes. That is faster and more robust than the old flow-then-warp chain — but the failure cases are still the same, because the underlying problem (guessing where things move) is unchanged.
The artifact language you need
- Ghosting: a semi-transparent double image where motion was ambiguous
- Warping: background stretching around a fast-moving object
- Occlusion: the model invents what's behind the object
- Flicker: per-frame inconsistency in synthesized frames
What it means for 60fps deliverables
Interpolating 24fps to 60fps genuinely doubles temporal resolution — motion becomes fluid. Used responsibly (not on film you want to look like film), it is the difference between a demo and a deliverable. Our interpolation API handles the flow and refinement internally, per content preset.
FAQ
Common questions
Is frame interpolation the same as motion smoothing on my TV?
Same idea, different execution: TV motion smoothing is aggressive real-time interpolation that produces the 'soap opera effect'. Production interpolation is done offline with better models and tunable strength.
Why does interpolation sometimes create ghosts?
When pixels cannot be matched between frames (occlusion, fast motion), the model guesses — and a blend of two guesses looks like a ghost. High-end models detect and repair these cases.
Can interpolation fix bad slow-motion?
It synthesizes in-between frames to smooth it, but it cannot add motion blur that was never captured — true slow motion needs high shutter-rate capture.
Keep exploring
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Frame Interpolation API
Smooth motion with AI frame generation — 24 to 60 fps.
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