Sure, you’ve heard of it. You’ve seen it in ads for camcorders, VCRs, and edit controllers. It’s time code.
But what exactly is it all about?
This article will help to answer some of the questions you may have about time code. It explains
what time code is, how it works, and how you can use it to achieve easier and more accurate edits. And it
that’s what you’re after, read on; more than likely, there’s time code in your future.
What is Time Code?
Time code refers to addressing, with a time value, the individual frames of a video recording. you can
use time code to start and stop an edit sequence, or to trigger special effects such as dissolves, digital
wipes, or animation sequences. It affords the most accurate timing for critical editing.
In one second, your camcorder captures thirty separate frames of video; time code assigns a
number to each frame. For example, if your time code matched the clock on the wall, and you start
recording at 8:30 in the morning, your first frame would have the number 08:30:00:00–hours, minutes,
seconds, and frames.
Or, you could use elapsed time, setting everything to zero when you start. Then your time code
would reflect the running time of the tape. Using this method, if frame number one were 00:00:00:00, then
ten minutes later you’d be at 00:10:00:00. There is no frame number 30, however–after 29, the code resets
What Good Is Time Code
Imagine how easy it would be to log your scenes before editing if you could keep track of each and
every frame on the tape. You could simply write down the beginning and end of each scene, do a little
subtraction and you’d have each scene’s exact length.
This is one thing time code does for you. It also helps you edit using an edit decision list, or EDL.
Armed with this list, you can let automated tape decks and effects hardware do the actual edits for you.
Pros call this on-line editing; off-line editing is when you make a rough cut and create the EDL. Using both
off-line and on-line is how most network television programs are edited.
Even small projects can benefit from time code. With code, every edit takes place exactly the way
you plan it–no cut off words, no unwanted single frames left in between edits. And if you’re after special
effects, they’ll come in right on cue.
Where Does Time Code Live?
Time code is a product of professional video, more recently adapted for consumer formats.
Professional machines have a linear address track called a CUE track–a part of the tape set aside
exclusively for longitudinal time code (LTC, see figure 1). But where do you put it on home video? Let us
count the ways.
8mm video formats have a place for time code. The record head writes data bits right next to the
PCM (pulse code modulation) audio. There are no linear tracks on 8mm tape–the rotating video heads
record everything diagonally.
Hi8 camcorders and editing decks use Sony’s own version of the code–they call it RCTC, or
Rewritable Consumer Time Code.
On S-VHS there’s only one linear audio track. If you put time code on it, you give up your audio.
So. . .
S-VHS solution number one: split the audio track into two. Many pro S-VHS decks have two
audio tracks, one of which you can use for longitudinal time code.
Some S-VHS videomakers put all their audio on the hi-fi tracks, and sacrifice the linear track to
time code. Since you lose the hi-fi audio during a video insert edit, this limits you to assemble edits only.
And most consumer edit decks do not have separate inputs and outputs for the linear track.
S-VHS solution number two: put the time code in the picture. Actually not in the visible picture,
but in the "vertical interval," the normally unseen video lines right above where the picture starts (see
figure 2a). Every 1/60th of a second, the video picture goes blank (too quickly for your eyes to notice).
During these "vertical blanking interval," your record heads can record both analog and digital data, such
as closed captions, transmitter test signals and additional audio tracks.
SMPTE code (pronounced "SIMtee" is the most universal of the time codes in current use. Each
vertical blanking period is made up of 21 scanlines. Time code is recorded on two non-adjacent lines in the
interval (see figure 2b), using the SMPTE time code standard. Developed by the Society of Motion Picture
and Television Engineers, SMPTE is a stream of digital pulses, or bits, at the rate of 80 bits per frame. If ,
in one second, 30 frames of video go by, you’ll have 2400 bits of time code.
SMPTE code put in the vertical interval is called VITC (VIT-see"), or vertical interval time code.
There’s one disadvantage to this type of code: it must be recorded as part of the video image. Hence it’s
mixed in during recording, and cannot be added later unless you dub the video to another tape, thus losing
VITC has one distinct advantage over linear code: it works at slow speeds, even when in pause.
This is one of the reasons broadcast editors have adopted it. Also, it’s not limited to the S-VHS format.
S-VHS solution number three: put time code on the control track. On all analog video tape
formats except 8mm and Hi8, a separate control track records along the edge of the tape. This track is
similar to the linear audio track, but contains only a single pulse every 1/60th of a second. Embedding time
code in this area is called CTL time code, and so far it has only been used by JVC on their Edit Desk
industrial editing system.
What is Control Track Editing?
In the world of VHS, every video frame has a corresponding control track pulse, and you can use
these pulses to keep track of where you are on the tape (see figure 1).
If your deck has a digital counter, one that reads in minutes and seconds, it’s probably counting
control track pulses. The timing from control track is relative to the beginning of the tape, or wherever it
was that you reset the count to zero.
8mm decks without time code use a counter system based on each line of video. As a result almost
every counting problem that will effect a VHS machine will also effect 8mm decks.
There are four ways to louse up the timing with control track editing:
- If you remove the tape and then reinsert it, most VCRs will reset the counter to zero.
- If your deck offers a high-speed rewind, the tape will partially unthread, away from the heads,
and it won’t pick up the control track or scan line information. The deck will try to estimate how far the
tape has moved, but accuracy suffers.
- If tape is blank, there will be no c control track pulses to count and the digital counter will
freeze in place.
- Finally, wrinkles, splices, and less-than-perfect tension on the tape can also cause the tape to lift from the control track head.
However, editing with the control track as your guide is not only simple, but inexpensive, and
(depending on the equipment you use) accurate to within a few frames. With two decks tied together so
that the record deck controls the playback deck’s pause mode, you can have basic control track editing.
You find the edit points manually, put the machines in pause, start the edit, and the VCRs will
count control track pulses to make the edits happen on time.
What is an Edit Controller?
Faster and more convenient editing is possible with a device called an edit controller. It’s a little box or
stand-alone console that hooks up to your decks (or camcorder), or it can be a hardware/software
combination controlled by the keyboard of your personal computer. It may use either control track or time
code to help you execute your edit commands.
As features and performance vary from one VCR model to the next, so do edit control protocols.
At least nine different protocols are out there, using anywhere from two wires on a mini-plug to a 45-pin
cable. More flexible edit controllers will work with a number of these protocols.
Edit controllers start at less than $200, but you can spend $2000 or more–and there are many
models to choose from. Most read LTC, VITC, or RCTC time code.
Time Code Editing–What Do I Need?
In order to use time code, you must write (or record) it on your original camera tapes. For that you
must have a time code generator; some top-of-the-line camcorders have them built-in. You’ll also need an
edit controller capable of reading the time code.
Some high-end Hi8 camcorders have RCTC time code generators and readers built in. This makes
a nice package with no external time code equipment needed. At least one consumer Hi8 deck, Sony’s
EVS7000, will also generate and read RCTC.
If you’re planning to shoot S-VHS, you’ll probably need to use an external time code generator.
Panasonic’s lowest-cost industrial camcorder, the AG-455, automatically records VITC every time you
shoot. You can’t set it to real time, or reset it manually–it starts at 00:00:00:01 and increments as you
record, resetting to zeros again after shooting 24 hours worth of tape.
You can always dub in LTC time code on the linear audio track of your S-VHS camera masters
just before you edit. This only works if you’ve shot without sound, or have your audio on the hi-fi tracks,
because the single linear track gets used for the LTC.
If you wish to stay in the S-VHS format and want time code without the audio track sacrifices,
consider JVC’s Edit Desk System–their BR-S500U source deck and BR-S800U edit recorder. They work
with their own edit controller, the RM-G800U, and use the previously mentioned CTL time code.
One more piece of equipment you may need is a regenerator. Since time code pulses can become
unreadable after only two generations of dubbing, this device was designed to recreate clean new pulses
from the old ones.
How Accurate is Time Code Editing?
The main reason for time code is accuracy. With only the control track to count, your edits may
execute too early or too late. The biggest problem with control track editing is tape slippage. Since your
VCR (or your camcorder) transport is nothing more than a mechanical device, it is prone to wear and tear
just as the tape is prone to stretch and dropouts. This results in periods of time where the system is unable
to read the control track. Even simple errors like this can throw the control track editor way off.
In theory, SMPTE code eliminates any possibility of error. If you select 00:10:12:04 as your edit
point, the edit will occur on schedule at frame number four, ten minutes and 12 seconds into the tape. If
you want to do the edit over, you can insert new video (or audio) right on top of the old stuff, and it will fit
The actual precision of your edits will be subject to the quality of the editing decks, edit
controller, and/or editing software.
For example, if you use Future Video’s V-Station 3300 as your edit controller, you can expect
(according to the manufacturer) +/-1 frame accuracy with SMPTE code, and +/-2
frames without time code (on S-VHS decks such as Panasonics’ AG-1960 and AG-1970). With Hi8
formats using RC time code, three-frame accuracy is common.
Good control track edit controllers should get you to within +/-5 frames without time code, and
+/-2 frames with RCTC time code. SMPTE time code-capable decks with a compatible controller should
render +/-1 frame accuracy. As you look for an editor, note that some companies do not advertise their
accuracy (or lack of it), regardless of the price they charge. If you require very accurate editing, try to test
the system before you buy.
We should note here that Sony’ RCTC time code does not number every frame–it skips some
frames in order to record the date and time of day information. If the edit controller doesn’t have code to
read, it will count incoming video frames until valid frame code reappears.
Sony’s professional Hi8 time code does not skip frames by design, and is essentially identical to
SMPTE code, though not recorded the same way. Its accuracy thus depends on the editing system you use,
and it is not compatible with RCTC time code.
While editing, you can use time code in-points instead of control track numbers to trigger your
editor’s general purpose interface (GPI). In this way, you can precisely time events from effects generators,
such as the Videonics MX-1, or Panasonic’s WJ-MX30. Then your dissolves, flips and other transitions
will come in right on cue.
Yes, upgrading to time code does cost money. You can purchase such items as in-line time code
generators and readers, or you can buy hardware which is already designed for time code rather than
adding to the equipment you already have. But remember, if you’re starting from scratch, it pays to get the
best you can.
Nonetheless, videomakers who use time code often say they could never live without it.