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Live Update mode updates images in the Composition or Layer panel during interactions. When Live Update is deselected, After Effects displays wireframe representations during interactions.
To turn Live Update mode on or off, click the Live Update button , at the top of the Timeline panel or use the Live Update menu item in the Timeline panel menu. (In recent versions of After Effects, the button has been removed, so the entry in the Timeline panel menu is the only means for toggling Live Update on and off.)