Time Code is On Your Side

William Ronat
September 1997

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."

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.

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.

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