Understanding timecode

on Wednesday, August 27, 2008

A video image is actually a series of still frames that flash rapidly by on-screen. Every frame is uniquely identified with a number called a timecode. All stored locations and durations of all the edits you perform on a movie project use timecodes for reference points, so a basic understanding of timecode is important. You’ll see and use timecode almost every time you work in a video-editing program like Pinnacle Studio or Apple iMovie. Timecode is often expressed like this:

hours : minutes : seconds :frames

The fourteenth frame of the third second of the twenty-eighth minute of the first hour of video is identified as:


You already know what hours, minutes, and seconds are. Frames aren’t units of time measurement, but rather, the individual still images that make up your video. The frame portion of timecode starts with zero (00) and counts up to a number determined by the frame rate of the video. In PAL video, frames are counted from 00 to 24 because the frame rate of PAL is 25 frames per second (fps). In NTSC, frames are counted from 00 to 29. The NTSC and PAL video standards are described in greater detail in Chapter 3. “Wait!” you exclaim. “Zero to 29 adds up to 30, not 29.97.”

You’re an observant one, aren’t you? As mentioned in Chapter 3, the frame rate of NTSC video is 29.97 fps. NTSC timecode actually skips the frame codes 00 and 01 in the first second of every minute, except every tenth minute. Work it out (you may use a calculator), and you see that this system of reverse leap-frames adds up to 29.97 fps. This is called drop-frame timecode. In some video-editing systems, drop-frame timecode is expressed with semicolons (;) between the numbers instead of colons (:).

Thus, in drop-frame timecode, the fourteenth frame of the third second of the twenty-eighth minute of the first hour of video is identified as


Why does NTSC video use drop-frame timecode? Back when everything was broadcast in black and white, NTSC video was an even 30 fps. For the conversion to color, more bandwidth was needed in the signal to broadcast color information. By dropping a couple of frames every minute, there was enough room left in the signal to broadcast color information, while at the same time keeping the video signals compatible with older black-and-white TVs.

Although the punctuation (for example, colons or semicolons) for separating the numerals of timecode into hours, minutes, seconds and frames is fairly standardized, some videoediting programs still go their own way. Pinnacle Studio, for example, uses a decimal point between seconds and frames. But whether the numbers are separated by colons, decimals, or magic crystals, the basic concept of timecode is the same.