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How exactly does 23.98 video work?
Hi, all!
So this is one of those questions that goes back and forth on the boards, and just need some help understanding this concept.
I understand that drop frame timecode doesn’t actually drop frames, but in order to compensate for the fact that certain frame rates don’t run at the same speed that would match a wall clock if counted without drop frames, the first two frames of every minute excluding 10-minute intervals are skipped when counting frames.
This makes perfect sense to me for 29.97 video. Ok, great.
Now, on the other hand, we have the fun of “24p” video, which, as I understand it, actually runs at 23.98 fps. What’s fuzzy to me is why, then, 23.98 video is counted using non-drop frame timecode. (I know this because in Final Cut, with 23.98 formats, it doesn’t even allow you to select drop-frame. This corroborates what other people have said in other posts as well about how video cameras use non-drop frame for their 24p modes).
And while we’re on the subject, is 23.98 fps video not an even number for the same reason that 29.97 fps video isn’t?
And if so, how can non-drop frame timecode actually represent time accurately?
Hope I’ve been articulate enough in asking, I know that a lot of people who have questions on this topic get flamed for it… But I’m just trying to wrap my mind around this thing.
Thanks!!!
Nick
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5 Replies
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[Dave LaRonde] “But those buffoons who worked out the standards for HD NTSC actually KEPT 29.97 when they could have gone with 30fps! Idiots! Maroons! Mouth-breathing imbiciles!”
Hey Dave, don’t hold back… let loose your inner frustrations!
Baz
What would I do without the ‘UNDO’ button!!!!
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“23.976” and “23.98” video is actually 24 * 1000 / 1001 frames per second. 23.98 is generally understood to refer to that, since there is no 23.98000 fps format. 29.97 video is 30 * 1000 / 1001 frames per second.
For 23.98 you also have to use non-drop frame timecode, which doesn’t keep in step with real time.
2- I believe they don’t broadcast HD at 30.00fps since you’d run into all sorts of sync issues. To simulcast HD and SD at the same time, it’s easier if both were at the same frame rate.
It’s pesky and annoying, but it’s a problem you can overcome.
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Just to add some clarification…
NTSC refers only to analog video.
ATSC is any of the SD and HD digital video formats.tim
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Hmmmm… Then why is the term “NTSC DV” used so prevalently?
Nick
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Sorry for the slim descriptions above — not too informative.
NTSC D1/DV and PAL D1/DV are all based on the analog 525-line NTSC and 625-line PAL standards, respectively. As I understand it, these formats were designed to work within the existing NTSC workflow, and were around before the ATSC formats were standardized. Notice how with the HD formats, there is no “NTSC” or “PAL” designation. The only sign of the different TV systems is the frame rate: 60i/30p and 50i/25p.
Someone with a much more though understanding of the inner workings of DTV is Mark Schubin< /a>. That’s one smart dude.
tim
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