Keyframes and Interpolation
Poses in time and how the computer fills in between
Also known as: Keyframe animation · Interpolation types · Bezier tangents · Stepped animation · Graph editor · Animation curves
Definition
A keyframe stores the value of a property, such as a bone's position or rotation, at a specific time. The software fills in the frames between keys by interpolation, which can be stepped, where the value jumps from key to key, linear, which moves at a constant speed, or spline and Bezier, which ease in and out along a smooth curve. Animators shape these curves in a graph editor, and the way they are set strongly affects the feel of the motion.
In production
Block the pose with stepped keys first, to judge timing without the computer smoothing it, then switch to spline and refine the curves. Avoid keys on every frame unless baking is needed. When exporting to engines, constraints and non-bone keys must be baked into bone transforms, and the engine's compression can change the curves, so check them. Clean curves are easier to edit and compress better.
Tools that use Keyframes and Interpolation
See also
The 12 Principles of Animation
Foundations of believable motion
Walk and Run Cycles
The looping base of character locomotion
Animation Compression
Reducing animation memory with a small error
Looping Animation Has a Hitch
A stutter at the point where a cycle repeats
Additive Animation
Layering motion on top of other animation
Animation Frame Rates (24, 30, 60 fps)
Which frame rate to animate and export at