What is frame blending in After Effects?

It is a layer setting that creates in-between frames when footage is slowed down or its frame rate does not match the composition, instead of repeating or dropping frames. You choose Frame Mix or Pixel Motion and enable it for the composition.

Frame Mix or Pixel Motion: which should I use?

Pixel Motion usually looks smoother for slow motion because it estimates motion; Frame Mix is a simple cross-fade that ghosts but never warps. Try Pixel Motion first and fall back to Frame Mix if you see warping.

Why is frame blending not working?

In After Effects, check that both the layer's frame blending switch and the composition's Enable Frame Blending button are on. In Premation, check the source frame rate is known; if it is not, set Interpret Footage ▸ Conform frame rate.

Glossary

Frame blending

Name: Premation
Author: Premation

Synthesising in-between frames when footage is slowed down or its frame rate does not match the composition, instead of duplicating or dropping frames.

Also called Frame Mix, Pixel Motion, Frame interpolation.

In After Effects

In After Effects frame blending is a per-layer switch in the timeline, set to Frame Mix or Pixel Motion (also under Layer ▸ Frame Blending). It only shows in previews when the composition's Enable Frame Blending button at the top of the timeline is on.

In Premation

Turned on automatically by a speed ramp below 100%; the Pixel Motion mode estimates optical flow on the GPU.

Step by step

Select the video layer you have slowed down or that has a different frame rate from the composition.
Choose Animation ▸ Time ▸ Frame Blend and pick Off, Frame Mix or Pixel Motion.
Or let a speed ramp set it for you: ramping below 100% turns on Pixel Motion automatically, unless you had set blending to Off.
If blending seems to do nothing on a mismatched frame rate, set Interpret Footage ▸ Conform frame rate to the footage's real rate, since blending brackets on the source rate.

Tips

Frame Mix cross-fades neighbouring frames: cheap and predictable, but it looks like ghosting on fast motion.
Pixel Motion estimates motion between frames and builds a new one. It is smoother but can warp edges where objects cross or move fast.
Without blending, 25% speed is each frame held four times, which reads as stutter rather than slow motion.
Nothing beats shooting at a higher frame rate. Blending is an estimate; real frames always win.

Walkthrough: Speed ramp and slow motion video

Read the docs: Speed ramps

Questions

What is frame blending in After Effects?: It is a layer setting that creates in-between frames when footage is slowed down or its frame rate does not match the composition, instead of repeating or dropping frames. You choose Frame Mix or Pixel Motion and enable it for the composition.
Frame Mix or Pixel Motion: which should I use?: Pixel Motion usually looks smoother for slow motion because it estimates motion; Frame Mix is a simple cross-fade that ghosts but never warps. Try Pixel Motion first and fall back to Frame Mix if you see warping.
Why is frame blending not working?: In After Effects, check that both the layer's frame blending switch and the composition's Enable Frame Blending button are on. In Premation, check the source frame rate is known; if it is not, set Interpret Footage ▸ Conform frame rate.

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