Re: [Avid-L2] Rookie TC question

On Oct 21, 2009, at 7:55 AM, Steve Hullfish wrote:

> Well, the frames are dropped in the NAMING of the frames, as you know,
> and not in the actual frames themselves. My analogy is that drop frame
> time code is like a skyscraper hotel where there's never a 13th floor.
> Of course floor 14 is ACTUALLY the 13th floor, but they named it 14.
> That obviously doesn't mean that there's a one floor hole in the
> skyscraper, or that just because you have a penthouse on the 21st
> floor, you're not REALLY only on the 20th floor.

On Oct 21, 2009, at 11:57 AM, Philip Hodgetts wrote:

> And to go with Steve's excellent explanation, an illustration:
> http://www.philiphodgetts.com/2009/10/20/what-is-drop-frame-timecode/

I now say:

This is what I commented on the above-referenced blog -
"Phillip, your diagram doesn't explain WHY there is a need for Drop
Frame Time Code. Here's my explanation:
The difference in the total number of frames between 29.97fps NTSC
video and exact 30fps video is approximately 108 frames per hour. IOW,
there are 108 FEWER frames of video at 29.97fps than there are in 30fps
video. In order to make 29.97fps NTSC video time code run at accurate
clock time (where an hour of video displays exactly one hour of DF TC),
those 108 frame numbers must be skipped so that the clock time (as
represented by time code) will 'catch up' to actual clock time and be
accurate at the end of the hour.
It was decided (I think SMPTE made this the standard) to skip 2 frames
every minute except on the tens-of-minutes. There are of course 60
minutes per hour. If you skipped 2 frames for each minute, that would
be 120 skipped numbers, which is too many skipped frame numbers. By
NOT skipping frame numbers on the tens-of-minutes, there would be 6
occasions when numbers would NOT be skipped each hour. Since each
skipping occurrence skips 2 frames, that means 12 frames would NOT be
skipped on those special instances. The result is 120 minus 12, which
is of course 108; the exact number of frames that must be skipped each
hour."

Dennis Degan, Video Editor-Consultant-Knowledge Bank
NBC Today Show, New York

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