In SMPTE video synchronization and post-production, the SMPTE time code addresses selected by the editor as the beginning and end points of a loop. The synchronizer will stop master and slave transports at the mark-out point after each insert take, then automatically return all machines to the mark-in point in preparation for another take. Various synchronizers automatically add pre-roll and post-roll times to the mark-ins and -outs, so it is important to understand how each unit internally defines all of these locations.