Adobe After Effects is what's known as a "composting" video program. Composting programs allow you to bring several disparate elements together, such as a 3-D computer model and live footage, and make it look as if they were all in the same video shot. Although the user interface may look complicated, there are a number of shortcuts to help users edit in After Effects. For example, it's possible to split video in After Effects into two layers with a few simple keystrokes.
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Import your video into After Effects. Go to the "File" menu in the upper-left corner and select "Import." Navigate to your selected footage file and click "OK."
Drag the footage from the "Project" files box in the top-left corner of the screen to the "Composition" box at the bottom of the After Effects widow. The footage file will show up as a new layer in the "Composition" frame.
Move the timeline marker to the point where you want to split the clip by dragging the handle at the top.
Press the "CTRL"+"SHIFT"+"D" ("CMD"+"SHIFT"+"D" on a Mac). The footage will split into two layers on your selected mark.