In the process, the original segments can be shortened and rearranged, bad shots can be removed, and audio and video effects can be added. These reference points are then entered as either control track marks or time code numbers. You then turn things over to the edit controller, which uses the precise beginning and ending points you've entered, to roll and cue the tapes and make each edit. I n simple linear editing systems the in and out points are referenced by pulses recorded on the tape 30 per second in NTSC video. The method of editing that locates and marks segments based on a count of control track pulses is referred to as control track editing .
Control track editing has two major shortcomings.
First, it relies on equipment to maintain an accurate count of thousands of control track pulses. For basically mechanical devices this can be difficult. During editing you are constantly shuttling tapes forward and backward at varying speeds as you find and mark in and out points for edits. If equipment loses count just for a fraction of a second, an edit point will end up being off by a few video frames which will destroy a carefully timed edit. Savvy editors keep an eye on the digital tape counter as tapes are shuttled back and forth.