The first video recorders used tracks that were perpendicular to the tape length, and editing could be accomplished with a razor blade and sticky tape. It was not as easy as it sounds, however. To make the tracks visible, a wet solution of tiny iron particles was spread on the tape. As the solution dried, the particles were attracted to the magnetized tracks, making them visible. The cut could then be observed with a microscope. Today's long diagonal tracks make this method impossible.

Here is a clip from 1960, edited with a razor-blade. The audio head was 3/4 of a second downstream from the video heads on these machines, so there is a 3/4 of a second video-before audio transition at every edit.

Making an edit on video tape is a matter of switching from play to record at the correct time, with no disturbance in the flow of tracks on the tape. Punch record on a standard VHS machine, and play back the result.

This is the result when a simple helical machine is made to go from play to record. The mess is subtle, but lasts for several seconds. It is caused by improper erasure of the old video, and is explained in the next section.

In a simple machine, the erase and audio heads are a significant distance from the head drum.

In most video recording machines, the tape passes the master erase head a few seconds before it reaches the spinning video heads. when the tape is switched from record to play, there is a section of tape already past the erase head. This tape gets a double recording (ugly). An editing machine has flying erase heads located on the drum. These flying heads can erase a diagonal track immediately before the record head reaches the track. An edit machine can actually replace as little as one pair of tracks (two fields = one frame) on the tape and leave the rest undisturbed. Here, the record heads are magenta, and the flying erase heads are blue.

Insert and Assemble

There are two editing modes available on an editing machine- insert, and assemble. Insert recording does what it says.... it will cleanly insert video and or audio on a designated section of tape without causing a disturbance.... just what we want, BUT, and it, as we say, is a big BUT: Insert mode needs a tape with pre-existing un-broken control track, and timecode (see next) information. For this reason, a tape to be edited in the insert mode must be "blacked". To "black" a tape we just record, in real time, as much video black as the program requires. A thirty minute program requires about thirty-two minutes of black to allow for some bars, and a slate at the start. There is no need to use black.... some people use bars or a bright colour so that they don't accidentally leave a blank frame in the project. In electronics, white is no harder to erase than black!

The assemble mode presumes that you are adding segments to the tape in a sequential fashion. It uses the master erase head to clear the whole tape, including the control track and timecode, which it records fresh. At the end of an assemble edit, there is a few seconds of NOTHING (the distance between the master erase head and the head drum). The advantage of assemble mode is only that the tape does not need to be blacked. Beware: an assemble edit where you wanted an in and out insert edit will ruin your show from the out point onwards.

Timecode

The day after video editing moved from the razor blade to the electronic world, a method of uniquely identifying each frame on the tape became a necessity. An edit is made on tape by cueing up a playback tape, and a record machine a few seconds before the edit point. The machines roll forward, and at the desired moment, the recorder switches seamlessly into record. (Whew!) ...or not. The earliest editing systems positioned the tapes by counting control track pulses... 10 seconds = 300 CTL pulses. Inevitably, one machine or the other would miss pulses as the tape slowed near the start and stop points, and the edit would be off by a few frames. Also, even two identical machines may be loaded with different sized tapes, and one may require longer to "get up to speed" than the other (ballistics). If that was a question, Timecode is the answer.

Timecode (SMPTE timecode) records a running time on each frame, in the hours:minutes:seconds:frames fromat... 01:23:12:14. Timecode also has room to encode "User Bits"... a few hexadecimal (0123456789ABCDEF) characters that can be used to identify the camera, or the reel number, or be totally ignored, which is the real truth about user bits.

It's important to realize, that the time such as 01:34:45:12 is actually recorded on the frame, and if asked to cue to that point, any machine will display exactly the same frame of the tape. Yes, you could index a photo album of 54,000 individual pictures on a thirty minute tape, and access any one of them by exact number (time on the tape).

Often, copies are made of a tape with a timecode display showing in the picture, so editing decisions can be made on a simple home machine. Using timecode, the editing machines can not only cue accurately, but any differences in "getting up to speed" can be compensated for.

LTC

It's pronounced "LIT-see". Linear Time Code. LTC codes the numbers into an audio signal that is recorded on a dedicated audio track of the tape, and is designed to be readable in high-speed searching, as well as at play speed. It sounds like this, only WAY louder if you accidentally patch it into your audio board!

LTC cannot be read at very slow speeds, or in still mode, so the following was invented:

VITC

"Vit-see" is Vertical Interval Timecode is embedded in the vertical interval of the video. It travels wherever the video travels, unless it is replaced by a unit like a processing amplifier that replaces the sync on the picture. VITC can be recovered during still, and very slow playback. Caution... on an edited tape, VITC is re-inserted every time a video edit is made. Unless the menu item "regen in insert and assemble" is set, the VITC will have useless, chopped-up numbers.

Machines that use both forms of timecode have a switch to force the reading of either kind exclusively, in case one is damaged. A dual timecode machine will use LTC for fast searching, and switch to VITC as it slows and stops.

Timecode is pretty simple, and you probably understand it, so you will be sorry to look at the timecode generator settings.

Free Run mode is meant to record the actual time of day to the tape. In this mode, a production assistant can log takes by looking at a wristwatch. It sounds great but is an extremely bad idea! The resulting tape has large gaps in the time (while you weren't recording) that cause all sorts of problems on an edit system.

Drop Frame

Recall that NTSC video runs at 29.97 frames per second, not 30. If the timecode is allowed to run ascending numbers at the rate of one per frame, an error of about 3.6 seconds per hour accumulates. Since we rely on the timecode display to tell us exactly how long our program is, Dropframe code is used in television. No frames are dropped! Only the frame numbers are missing.

Dropframe omits the frame numbers 00 and 01 every minute, except on multiples of 10 minutes. 108 frame numbers are dropped every hour. Remember, this is a good thing, and none of your precious frames are actually missing... just the numbers! Editing systems handle dropframe code painlessly.