In-betweening

What is In-betweening?

In-betweening is the process of filling in the frames between the key poses in an animation so that movement flows smoothly rather than jumping abruptly from one position to the next.

At a glance

Also known as
TweeningInbetweening
Used for
Creating smooth motion between keyframes in animationFilling transitional frames in hand-drawn or digital animation pipelinesGuiding AI video model frame interpolation quality
Common tools
Adobe animateToon boom harmonyAfter effectsBlenderAI video generation models with frame interpolation
Related terms
KeyframeTweeningFrame rateAnimationInterpolation

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How it compares

How it compares

Compared with related concepts

In-betweening is distinct from keyframing, which refers specifically to the process of defining the significant pose moments. Keyframing establishes the dramatic structure of a movement; in-betweening connects those moments into fluid motion. Without quality in-betweening, even beautifully drawn key poses produce stilted, choppy animation. The relationship between the two is analogous to the difference between plotting the key story beats of a scene and writing the dialogue that connects them.

Think of it like…

In-betweening is like filling in the steps between photographs on a time-lapse: the key photos capture the important moments, but it is the intermediate steps that make the overall movement feel smooth and continuous rather than jumpy.

Pro tip

When evaluating AI-generated video for animation quality, pay close attention to the arcs of movement between positions: good in-betweening follows smooth curved paths rather than straight lines, giving motion an organic, weighted quality that reflects the principles of animation. If generated motion feels stiff or mechanical, try adding descriptive language about the desired quality of movement in your prompt: phrases such as 'smooth, fluid motion with natural ease-in and ease-out' can meaningfully influence how the model handles transitions between states.

Types and variations

  • In-betweening can be performed manually by artists drawing each intermediate frame by hand, or automatically through software interpolation.
  • Digital in-betweening uses different interpolation methods ( linear, ease-in, ease-out, and ease-in-out ) to control the character of motion between keyframes.
  • AI-assisted in-betweening, increasingly common in modern animation pipelines, uses machine learning models to generate plausible intermediate frames, potentially reducing the labour required for this traditionally time-intensive task.

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Common use cases

  • In-betweening is central to all forms of frame-by-frame animation, from theatrical feature animation to television series, motion graphics, and game cinematics.
  • It is used whenever smooth motion needs to be created between defined key poses or states, including character movement, object animation, camera movement transitions, and visual effects such as morphs and transformations.
  • In AI generation contexts, understanding in-betweening informs how creators describe and evaluate smooth versus stiff motion in generated video, helping them communicate the quality of movement they expect and identify when generated footage falls short of natural motion principles.

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FAQs

What is in-betweening in animation?
In-betweening is the process of creating the intermediate frames between the key poses in an animation, filling in the transitional drawings or positions that produce smooth, continuous motion. In traditional animation, this was done by hand; in digital animation, it can be automated through interpolation software.
Why is in-betweening important?
In-betweening is what transforms a series of static key poses into fluid, believable movement. Without well-executed in-betweens, animation appears choppy and unconvincing regardless of the quality of the key poses themselves. The spacing, arc, and timing of in-between frames directly control the weight, speed, and naturalness of the resulting motion.
What is the difference between in-betweening and tweening?
The terms are essentially synonymous. Tweening is simply a shortened form of in-betweening, derived from the phrase 'in between.' Both refer to the process of generating or drawing the intermediate frames between defined keyframes in an animation.
How does in-betweening work in digital animation software?
Digital animation software calculates in-between positions automatically using interpolation algorithms. The animator defines the position, scale, rotation, and other properties of an element at two or more keyframes, and the software generates the intermediate values for every frame in between. The shape of this interpolation ( linear, eased, or custom ) controls the feel of the resulting motion.
What is AI-assisted in-betweening?
AI-assisted in-betweening uses machine learning models to generate plausible intermediate frames between two reference images or animation frames. This approach can significantly accelerate the in-betweening process, which is traditionally labour-intensive, by automatically predicting how forms should transition between states rather than requiring artists to draw every intermediate frame manually.
How does understanding in-betweening help with AI video generation?
AI video generation models perform an automated form of in-betweening as they generate motion within a clip. Understanding the concept helps creators write better prompts by thinking about the quality of movement between states: specifying smooth, gradual, or eased transitions helps shape how the model interpolates between visual states in the generated footage.
What makes in-betweening good or bad?
Good in-betweening follows the principles of animation: smooth arcs, appropriate spacing that reflects acceleration and deceleration, natural follow-through of moving parts, and overlapping action. Poor in-betweening follows straight-line paths between positions at constant speed, producing stiff, robotic motion that feels unnatural and lacks weight.
Is in-betweening only relevant to hand-drawn animation?
No. While in-betweening originated in hand-drawn animation, the concept applies to all forms of frame-by-frame motion. Digital 2D animation, 3D computer animation, motion graphics, and AI video generation all involve the same fundamental challenge of creating convincing motion between defined states, and the principles of quality in-betweening apply across all these formats.
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