Drop-frame vs. Non-drop-frame Timecode

[ This article was first published in the May, 2007, issue of
Larry’s Final Cut Pro Newsletter. Click here to subscribe. ]

When Durations Don’t Match in Viewer and Canvas
I ran into this problem recently where I had a clip in the Viewer with a duration of 2:00:00, but when I edited it into the Timeline, the duration jumped to 2:00:04.

Why didn’t they match?

The answer lies in the difference between two different versions of timecode – drop-frame and non-drop-frame. (You PAL and HD folks can nap thru this discussion — drop-frame timecode only applies to NTSC video.)

First, let’s define timecode: it’s a label that uniquely identifies every frame of video and/or audio. Timecode does not necessarily represent time-of-day. Rather, think of it as a name for each frame — a name that is expressed, not in words, but as a time value.

When television was first invented, all timecode was non-drop-frame. This meant that every frame of video had it’s own unique timecode label and the timecode value of each frame was exactly one frame larger than the previous frame.

The benefit of timecode was that if you knew the beginning and ending timecode of a program, you could quickly calculate how long the program ran in real-time.

Life was grand… until color television was invented. The problem with color was that it took 0.03 seconds every second to transmit the color information in the signal. While three-one-hundredths of a second doesn’t sound like much, over the course of a one-hour show, it added up.

Specifically, it added up to 3.59 seconds (almost a minute and half over an entire day)! Meaning that you could no longer count on timecode to provide accurate timing for a show.

Well, this was intolerable. I mean, if you couldn’t count on timecode, what could you count on?

So, a new form of timecode was invented: drop-frame timecode.

In spite of what the name implies, NO video frames are dropped using drop-frame timecode. What’s actually being dropped are some of the timecode labels. Your video is safe — whew!

The rule of drop-frame timecode is: two frames of timecode are dropped every minute, except on the tenth minute, when nothing is dropped. This means that over the course of an hour, 108 timecode labels are skipped. The exact numbering goes: 59:28, 59:29, 1:00:02, 1:00:03… (Notice two timecode labels were skipped: 1:00:00, and 1:00:01.)

With that as background, you can probably guess the solution. The clip in the viewer was using non-drop timecode, while the sequence was using drop-frame.

You can tell what timecode your sequence is using by going to: Sequence > Settings > Timeline tab and looking at the timecode check box. If Drop-frame is checked, you are using drop-frame timecode. If not, you are using non-drop-frame.

By the way, almost all DV video uses drop-frame. And remember, there is NO difference in quality or content between drop and non-drop timecode.

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