At first glance, time code may seem mysterious, but it’s really a common workhorse in video and film production. Without time code, many types of edits would be impossible to achieve, and others would take more effort than they should.
Time code gives each frame of video a unique "name" so that you (or anyone else) can find whatever scene you want. With time code, you can go through raw footage, pick a scene, take down the time code of the frame at the beginning of the scene and the time code of the frame at the end of the scene, and you have defined that scene. If you hand those numbers (and the tape that goes with them) to someone who knows nothing about your project, that person can edit the scene perfectly. If you define a whole bunch of scenes using time code, you create an edit-decision list (EDL), which you can use to put together an entire show.
Time code is the way video professionals make sure they are "reading off the same page." It’s much more precise to use a set of numbers to describe a video scene than to tell a service bureau to edit "the shot on tape 2, about 10 minutes in, where the dog does a somersault. Hmmm…at least I think it was on tape 2."
Frames and Numbers
Each second of video consists of 30 frames. With time code, you can give each frame a unique number. The numbers consist of hours, minutes, seconds and frames. On a professional VCR’s time-code display, here’s what they look like: 01:22:33:11 (one hour, twenty-two minutes, thirty-three seconds and eleven frames).
You might think, "What’s the big deal? My ordinary home VCR displays numbers as the tape plays. Why can’t I take those numbers down and use them to create an edit-decision list?" The problem with these numbers is that they’re usually just counting time, and will change if you remove and reinsert the tape. But with most types of time code, every frame always keeps the same time-code number, no matter when or where you play it.
Time code is a very handy tool for the video producer, but most camcorders and VCRs cannot generate, record or read it. Adding to the confusion is that different manufacturers and different formats record time code using different (and unfortunately, incompatible) methods. Let’s take a look at some of the different types of time-code systems.
Don’t Drop That Frame
Time is relative, and thanks to a decision by the National Television Standards Committee (NTSC), so is time code. You may run into the terms drop frame and non-drop frame. The difference between these types of time code could be important to you if you are creating a program that must be exactly one hour long (or exactly any other length).
Here’s why. The original black-and-white TV programs had exactly 30 frames per second. But to include color information, the NTSC determined that color television signals would run at 29.97 frames per second rather than 30 frames per second. But non-drop-frame time code assigns a number to 30 frames per second. This introduces an error of .03 frames per second. On an hour-long program, you would have an error of 3.6 seconds. Oops.
Drop-frame time code throws out the numbers at :00 and :01 frames at every new minute, except at the 10-minute marks (10 minutes, 20 minutes, 30 minutes, etc.). It doesn’t throw out any video content–just the numbers, to keep the run time of the time code equal to real time.
Where Does Time Code Live?
Even though all types of time code appear the same on the display panel (00:00:00:00), they differ in the way they are recorded onto videotape.
You can insert time code directly into the video signal itself, in an invisible part of the video signal known as the vertical interval. This vertical-interval time code (VITC) must be recorded at the same time as the picture. And you can’t copy VITC time code directly from one tape to another. To copy VITC, you must send the video signal through a regenerator. The regenerator outputs a clean, new VITC signal, which you can then record to a new tape.
Longitudinal time code, on the other hand, is a separate signal that you can record onto a separate linear track that runs along the length of the tape. The best-known type of linear time code is SMPTE (developed by the Society for Motion Picture and Television Engineers). You can record SMPTE onto the monaural linear audio track on a VHS or S-VHS tape, but not onto the hi-fi track.
Not to be outdone, Sony developed two proprietary types of time code: rewriteable consumer time code (RCTC) for consumer 8mm/Hi8 equipment, and industrial 8mm time code for industrial/professional 8mm/Hi8 equipment. Sony set aside a particular sector of the tape to hold either of these types of time code without disturbing the video or audio signals. RCTC and 8mm time code are not compatible with each other. The main difference between them is that industrial 8mm time code is guaranteed to be frame accurate; RCTC is not. Officially, RCTC is accurate to within +/- 2 to 5 frames, though half the time it’s right on the money.
If you do all of your production in-house using your own equipment, then you should be able to pick a particular time-code system and buy gear that’s compatible with that kind of time code. But if you shoot your own footage and take it to a service bureau to edit it, you could run into trouble if the service bureau uses a different time-code system. There’s a question that’s worth a phone call.
Time code not only affords accurate edits, it can also help you protect your precious original footage.
If you use your original video footage for editing, all that jogging back and forth to find and log scenes can put lots of wear and tear on the tape. Instead of risking the quality of your original footage, you can create what’s called a “window dub” for review. To create a window dub, you play back the original footage while a time-code reader superimposes the numbers onto the screen. When you record this onto another tape, it shows all of your footage with the time code numbers "burned-in" on top of it. (If you’re using a service bureau for your editing, ask if they can make a window dub using your type of time code.) The window dub is not useful for final product (you can’t get rid of the numbers once they are burned-in), so you can treat it with contempt. Shuttle back and forth until the tape is as thin as tissue, it doesn’t matter–it’s only a window dub. Your original stays in the box, pristine and unscathed, until it’s time for the final edit.
Preparing for a complicated edit session is easy with time code. All you need to do is make a list of which scenes you want to keep and which scenes, figuratively speaking, end up on the cutting-room floor.
View your window dub until you see the shot you like and pause the tape where you want the edit to begin. Write down the numbers that appear on the screen. Now let the tape run until you find the end of the shot. Write down this new set of numbers. Put a brief description of the shot next to the numbers. Do this for every “keeper” scene and you’ve made an EDL.
Maybe you have editing software or a stand-alone edit controller that can read time code. If so, you can perform the process this way: run the tape until you find the shot. Punch a button that saves the time-code number into the computer memory. Find the end of the shot and punch a button to save the end time. If you’re using a computer-based logger, you might be able to type in a description of the shot, or even save a small graphical image from the video (a "picon") to identify the clip visually.
Whatever method you use to log your footage, the logging step can save you time and money if you plan to edit at a service bureau. If the clock is ticking (and you are paying for each tick), you don’t want to waste this time searching for footage.
Once you’ve logged all your shots, you have the main ingredients to cook up an edit-decision list (EDL). With a paper EDL, you arrange your shots in the order that you want them in the final edited show. If you take all of your raw footage to a service bureau and give these numbers to the person who is pushing the buttons, you can get through the session in the smallest amount of time.
If you have a system that can save time-code numbers as you create your EDL (such as a computer-based system), you may be able to save the electronic EDL on a floppy disk and hand this EDL to the service bureau. If the bureau’s equipment is compatible, they can feed the EDL into the their equipment and assemble the show automatically. Of course, you will still want to add titles, sound effects, music and so on, but an EDL can still save a lot of time.
Computer Animation and Music Videos
Time code is also necessary for computer animation that is too complex to play back in real time. To capture complex animation, the computer must render each frame and then prompt a frame-by-frame VCR to record these frames onto tape, one at a time. Without time code, this process would be impossible. Control-track edits might get you within several frames, but could not achieve consistent frame accuracy.
Accurate editing is often important for music videos. If you are adding video clips to existing music and want certain parts of your shot to happen on the beat of music (the basketball goes through the hoop just as the cymbal crashes), then you will have an easier time of it if you use time code.
Even if you’re going to digitize your footage and edit it using a computer system, time code is still important. Using software, you search your raw tapes for the shots that you want to use. You mark the begin and the end times of the shots (by hitting a key) and the software notes and saves these time codes. You can also describe each shot (dog1, dog2, cat with mouse toy, etc.).
When you have chosen all the shots that you are going to work with, you can tell the computer to "batch digitize" your footage. While you go off to do something more productive, the computer finds the shots that you selected and converts them into digital information. Of course, you still have to change out the tape cassettes if your footage isn’t all on one cassette, but that’s a small price for this much automation.
Time code is about precision. With it, you can catalog your video down to 1/30th of a second and find specific shots–even frames–again when you need them. The operative word in time code is time, because that is what you will save by using it.
[SIDEBAR: Glossary of Terms]
- Control Track Electronic pulses that correspond to frames of video. Unlike time code, control-track pulses are not unique to each frame.
- Edit Decision List (EDL) A list of all the shots that you want to include in a video production. For each shot, the list usually shows the time code of the first frame and the last frame, and a short description. It may also include instructions for triggering titlers, special effects generators, etc.
- Frame Moving video consists of still pictures that display in rapid succession, creating an illusion of movement. There are 30 still pictures per second of video. Each of these pictures is a frame.
- Industrial 8mm Time Code A frame-accurate time-code system developed by Sony and available on all industrial 8mm and Hi8 camcorders and decks. It is incompatible with RCTC.
- Rewritable Consumer Time Code (RCTC) A time-code system developed by Sony and available on some consumer 8mm and Hi8 camcorders and decks.
- SMPTE Longitudinal Time Code Time code that can be recorded on a linear track on videotape, including a linear audio track.
- Time A commodity that Albert Einstein showed to be relative to the speed of light, and one that is almost always in short supply.
- Vertical Interval Time Code (VITC) Time code signal that is recorded in the "invisible" part of the video signal, the vertical interval.
Sidebar: The History of Time Code]
They can put a man on the moon, but can they create a system that can perform frame-accurate editing? Actually, they did. NASA used time code before anyone thought of using it for editing. The space agency created the system to keep track of all the information from their instruments (it was recorded onto telemetry tapes). A firm called the Electronic Engineering Company of America modified the system for use with videotape and put the first editing systems on the market in 1967. Other companies came out with competing versions, which prompted the Society of Motion Picture and Television Engineers (SMPTE) to step in and standardize the format in 1972.
[Sidebar: How to Make Your Own Time-Code Window Dub]
All you need to make a working window-dub copy of your existing footage for editing is two VCRs (one with time code), a video camera and a video mixer or SEG (such as the Videonics MX-1 or the Panasonic WJ-AVE55).
- Run the output of the source VCR (the one with time code) together with the video camera’s output through your video mixer; then run the output of the mixer to a record VCR.
- Point the video camera at the time-code display of the source VCR.
- Using the mixer’s picture-in-picture or vertical wipe feature, record the VCR’s time code numbers together with the output from your source tape onto the record VCR (see illustration). Be sure to make the time-code numbers visible, but be careful not to block significant portions of the screen.