An AET file is typically understood as a reusable AE template, 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.
What it usually doesn’t include is the raw media itself; instead it keeps references or paths to external footage, images, and audio, which is why templates are often delivered as a ZIP with an assets/Footage folder and why you’ll see missing-file prompts if items were renamed or not synced, and because AETs may rely on specific fonts or third-party plugins, opening one on another machine can trigger substitutions until everything is installed or relinked, with the final reminder that although AET typically means an After Effects template, file extensions aren’t exclusive, so checking "Opens with" in file properties or recalling where the file came from is the safest way to
confirm what program created it and what extra files it should include.

An AEP file serves as the main editable project file in After Effects, updated as you import footage, adjust comps, and refine effects, while an AET is a template meant as a reusable starting point, so the practical difference is workflow: you reopen an AEP to keep editing the same project, but you open an AET to create a new project so the template stays untouched.
That’s why AET formats are commonly packaged in motion-graphics template sets like intros, lower-thirds, and slideshows: the AET remains the creator’s master, and for each new video you open it, Save As a new AEP, then swap in your own text, media, logos, and colors, and even though both formats store the same project components—comps, layers, keyframes, effects, expressions, cameras/lights, and settings—and both usually reference external files, the AET safeguards the layout while the AEP becomes the editable end-user project.
An AET file preserves 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.
On top of that, the template retains all effects and their settings—color correction, blurs, glows, distortions, transitions, and more—along with any 3D setup such as cameras, lights, 3D layer properties, and render/preview settings, plus project-level organization like folders, label colors, interpretation rules, and sometimes proxies, but it typically does not bundle full footage, images, audio, fonts, or plugins, instead keeping links and dependencies that may trigger missing-asset or missing-plugin warnings on another computer until everything is relinked or installed If you beloved this short article and you would like to obtain far more details relating to
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