An AEP file serves as an Adobe After Effects project container that stores the structure of your work rather than a finished video, holding compositions, layers of all kinds, animation data like keyframes and expressions, effects with settings, masks, mattes, and even 3D tools such as cameras and lights, while usually referencing external media through file paths instead of embedding footage, which keeps the AEP itself lightweight even when the project uses huge amounts of video or audio.

Because AEP files don’t embed footage, After Effects can throw "offline media" warnings if you relocate or rename the assets or copy only the AEP to another computer without its media, making Collect Files—or manual gathering of all referenced items—the safest way to move a project, and if an AEP won’t open in AE, details such as where it originated, what’s stored beside it, Windows’ "Opens with," or a quick text-editor look can reveal if it’s a standard AE file or something from another software vendor.

When an AEP loads without footage on a second computer, the reason is usually that it’s a blueprint referencing outside media instead of embedding it, and After Effects uses absolute file paths for video, images, audio, and proxies, so once the project is moved to a machine with mismatched paths—different drives, folder names, or missing files—AE can load the structure but not the assets, yielding Missing/Offline Media until relinking.

If you want to find out more info about AEP file opener review the page. A project may look partially missing even with footage intact when the new machine lacks specific fonts—forcing text to substitute—or missing plugins that leave effects unreadable, or when using an older After Effects version that can’t interpret newer features, and the dependable solution is to use Collect Files or replicate the folder layout exactly and then relink, at which point matching fonts, plugins, and paths generally restore the project immediately.

An AEP file is essentially a small structural database that captures your entire After Effects project without containing the heavy media, storing comp properties like resolution, frame rate, duration, nesting, and background color, every timeline layer and its transforms such as spatial settings, scale, rotation, opacity, blending, mattes, parenting, timing, plus all animation instructions like keyframes, easing curves, motion blur, markers, and expressions, along with complete effect configurations and any mask or roto data including mask paths, feather, expansion, and animated vertices.

Using 3D in AE means the AEP saves your cameras, lights, 3D-layer attributes, and render settings, plus project-structure info like bins, label coloring, interpretation settings, and proxy references, but not the source media itself—videos, stills, and audio live outside the project—so the AEP acts as the blueprint and the file paths for your assets, which is why moving or renaming them leads to missing-media notices until you relink.