An AET file is mainly recognized as an After Effects template project, designed so you can open it repeatedly and save new versions rather than overwrite the source, with the file storing everything that defines the motion graphic: comps, timeline structure, layer stacks, animation keyframes, effect setups, expressions, cameras/lights, render settings, plus organizational items like folders and interpretation settings.

For more info on AET format check out our page. An AET generally doesn’t embed media, instead storing references or paths to external audio, images, and video, which is why template sets are bundled as ZIPs with Footage/assets folders and why After Effects reports missing items if things were moved, and because AETs might rely on certain fonts or plugins, opening them elsewhere can trigger alerts until everything is installed, and since file extensions aren’t exclusive, checking "Opens with" or the file’s source location is the best way to confirm the program behind it and what extra files should accompany it.

An AEP file acts as your active After Effects project, letting you import assets, edit compositions, and tweak effects over time, whereas an AET is designed as a template to be reused, making the key distinction that you update an AEP directly but open an AET only to start a fresh project based on it without altering the master.

That’s why AET files are typically used for template-based motion graphics (intros, lower-thirds, slideshows): the master AET stays unchanged while each new project starts by opening it and doing a Save As to create your AEP, where you modify text, colors, logos, and media, and although both formats include the same elements—comps, layers, effects, keyframes, expressions, cameras/lights, and settings—and both rely on external footage paths, the AET is meant for safe templating and repeatable output, while the AEP is the editable project you keep refining.

An AET file retains the structure and animation logic of an After Effects project but not always the media assets, containing compositions with defined resolution, FPS, duration, and nesting, plus the complete layer arrangement—text, shapes, solids, adjustments, precomps, and placeholders—with layer properties like position, scale, rotation, opacity, masks, mattes, blending modes, parenting, and the project’s animation data including keyframes, easing, markers, and any expressions used to automate motion.

Additionally, the template captures effects and their configurations, such as color correction, blurs, glows, distortions, and transitions, together with any 3D setup—cameras, lights, 3D layer settings—and render/preview preferences, plus project structure like folders, labels, interpretation settings, and proxies, though it usually omits embedding raw media, fonts, or plugins, depending on linked paths that can lead to missing-footage or missing-effect warnings when the file is opened elsewhere.