Compositions, layers and the timeline

After Effects organises work into projects, compositions and layers. Understanding how they relate makes everything else easier.

Projects and compositions

A project file holds all your imported files and compositions. A composition, usually called a comp, is like an artboard with a timeline: it has a width, height, frame rate and duration. For interface work, create comps that match your design size, for example 1170 by 2532 pixels for a phone screen at 3x, or simply at 1x such as 390 by 844 if you want lighter files.

Choose a frame rate of 60 frames per second for smooth interface motion, or 30 if file size matters more. Keep it consistent across the project.

Layers

Everything in a comp is a layer: imported images, shape layers, text layers, solids, nulls and other comps. Layers stack in the timeline panel, with the top layer appearing in front.

Each layer has transform properties, revealed by twirling down the layer or with shortcuts:

• P position
• S scale
• R rotation
• T opacity
• A anchor point

Press U to show only properties that have keyframes, which keeps the timeline readable.

Anchor points

The anchor point is the pivot for scale and rotation. A button that should shrink toward its centre needs its anchor point in the middle. A sheet that should scale from the bottom edge needs it at the bottom. The Pan Behind tool (Y) moves the anchor point, and Ctrl + Alt + Home on Windows or Cmd + Option + Home on macOS centres it on the layer content.

Precomposing

Select layers and press Ctrl or Cmd + Shift + C to precompose them into a new comp nested inside the current one. Precomps keep complex scenes manageable, for example one precomp per screen, which you then animate as a whole during transitions.

The work area and previews

The work area defines what plays during preview. Press B and N to set its start and end at the current time. Press Space to preview. If playback stutters, lower the preview resolution to half or quarter in the composition panel.

Keep it organised

Create folders in the project panel for imports, precomps and final comps. Name layers clearly. A tidy project matters when you return to it weeks later to update a single screen.