Re: [Avid-L2] Rookie TC question

Huh? DDD that does not explain why only what. You have to do the math
down from the colour sub-carrier if you wish to explain why.

DD

Dennis Degan wrote:
>
>
>
> 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/
> <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
>
>

--
David Dawkins
780-905-9121
dawk2@shaw.ca

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