Compositing Layers, Keyframes, and Animation
Stacking and switches
Compositing questions center on stacking order, layer switches, and time. Higher layers cover lower ones; blending modes and track mattes modify that relationship. Track mattes (alpha, alpha inverted, luma, luma inverted) require the matte layer directly above the affected layer, and that matte layer's video switch is disabled automatically. Parenting, usually to a null, makes children inherit a parent's transform while keeping their own values relative.
Keyframe mechanics
Every keyframe carries a value and an interpolation type: linear, Bezier, continuous Bezier, hold, or Easy Ease. The Graph Editor separates Value and Speed graphs, which is where easing is refined. Hold keyframes cannot be eased. Roving keyframes shift timing spatially between neighbors. Anchor Point and Position are different properties: changing the anchor point after animating position makes the layer jump unless you compensate.
Traps
- Motion blur requires both the layer switch and the comp switch.
- Changing composition duration truncates or extends the timeline but does not rescale existing animation.
- Time Remapping must be enabled (Layer > Time > Enable Time Remapping) before keyframes appear.
- Collapse Transformations changes how nested comps render and interacts with 3D and continuously rasterized sources.
Rule of thumb
Set the anchor point first, then position, then animate scale and rotation around it. To ease a selection quickly, select keyframes and press F9, then open the Graph Editor to shape the speed curve. When a layer must be stretched in time, use Time Stretch or Time Remapping deliberately rather than stretching the composition.