With Import you can add an existing video to your timeline as a clip. After you import the video, you can add captions, a different Shape or Frame color, and edit the clip in your timeline.

With Replace, you can swap out the rear camera for a video and record with this video as your backdrop. You can select a layout that combines your selfie camera and the video with a picture-in-picture or green screen effect, or your only show a single video source to record a voice-over.