Precomps (precompositions) nest one composition inside another — they help organize complex projects and let you apply effects to groups of layers at once.
Steps to create precomps
Select the layers you want to group together in your timeline. Right-click and choose Pre-compose. A dialog box opens asking you to name your new precomp and choose options.
Click OK and After Effects creates a new composition with your selected layers inside it. Your original comp now shows the precomp as a single layer instead of all those individual layers cluttering the timeline.
Double-click the precomp layer to enter it and see all the nested layers inside. You can edit them here just like a normal comp. When you’re done, click the back arrow or the main comp tab to return to the parent composition.
One more thing
Use precomps to keep your timeline clean and your projects organized. If you have 50 layers and group related ones into precomps, your main timeline becomes way easier to navigate and animate.
Related how-tos
How to set up a composition in After Effects
How to set composition resolution, frame rate, and duration in After Effects
How to organize assets in the Project panel in After Effects
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