Although I come from a country where we count frame rates in whole numbers and, therefore don’t need to skip frame counts in the timecode, I thought I understood it at least as well, or better, than “NTSC natives”. That is, until I really, truly had to understand it to ensure the reported time counts in Sequence Clip Reporter are accurate.
Well, it took three pieces of additional information before I truly understood it: Rainer Standke’s insistence that “frame is a frame is a frame”; the realization (although known) that 29.97 is actually slower than 30 fps with the consequence that each frame runs slightly longer than at 30 fps; and that the correction can’t be applied evenly.
At one level I knew all of these things, but it really all came together when I got the “right” mental picture. Since I could not find any illustrations that showed why the skip-frame timecode (a better term than drop frame imnsho) needed to skip frames, I decided to create this one. It’s licensed with a Creative Commons – Attribution license. That means you can reproduce it, or use it for any purpose as long at the attribution to me remains.
Not shown on the image is that the 2 frame skip-forward happens at every minute, except ever 10 minutes. There are other parts to the pattern as the timescale gets longer.