🚀 go-pugleaf

To lock-off a shot means to put your camera on a solid tripod so that it can't/won't move at all.

Film yourself sitting in one shot, and then film yourself standing and talking in the same shot without moving the camera.

From post #5, it sounds like you already did that.

To make the line go away, reset the Motion parameters so that each clip is full frame. Then add a wipe transition to the top clip and stretch it so that it runs the whole length of the clip. In the Effect Controls window, set the start and end of the wipe to be the same, positioned where you want it. Set the border width to 0 (the default) and anti-aliasing quality off (also the default).