An AET file acts as an Adobe After Effects template project, intended for repeated use so you open it, save a new project, and customize that copy, while the template stores the construction plan of the animation including comps, timelines, layers, keyframes, effects, expressions, camera/light settings, render configurations, and all the folder/interpretation organization that holds the project together.
What it usually does not store 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 left out 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 is the editable AE project you save and revise, holding all your comps, effects, and imported media, whereas an AET is intended as a template, meaning you reopen an AEP to keep editing but open an AET to launch a new project so you don’t overwrite the template.
That’s why AET formats are frequently bundled 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 is designed to store the structural and behavioral blueprint of an After Effects project rather than the actual media, including compositions with resolution, frame rate, duration, and nesting, plus the complete timeline layout with layers for text, shapes, solids, adjustment items, precomps, and placeholders, alongside properties like position, scale, rotation, opacity, masks, mattes, blending modes, parenting, and all
animation data—keyframes, easing, markers, and expressions when used.
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best app to open AET files review the web-page. On top of that, the template remembers 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.