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Comment by jhallenworld | Hacker News Reader

I'm not sure I understand this:

"The NTSC variations (~29.97, etc) are actually defined as 24 * 1000/1001 and 30 * 1000/1001, which are impossible to represent exactly in a way where 1 second is exact, so we don't bother - they'll be inexact in any circumstance."

The NTSC color subcarrier is exactly 315/88 MHz, so one could make the flick something like 1/528th of this period. The frame is related to the subcarrier by 525 lines by 455/2 color clocks.

See: https://en.wikipedia.org/wiki/Colorburst

So one NTSC frame is exactly 63063 flicks, one 30 Hz frame is exactly 63000 of them, one 24 Hz frame is 78750 of them and one second is exactly 1890000000 of them.

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I agree with your line of thinking, but since they give 1/30 fps frame as 23520000 flicks, I get 1 NTSC frame = 23520000 * (1001 / 1000) flicks = 23543520 flicks.

I was all set to file a doc PR but noticed you have to file a CLA. newp.

It is worth noting that while you can represent single NTSC frame time exactly in Flicks, it still does not fulfill their goal of representing "also 1/1000 divisions of each" for NTSC. To get there you'd need 1 Flick to be 25 times smaller, i.e. 1/17640000000 seconds. Although this would go below 1 ns, which was also one of their constraints, but I'm not exactly sure what importance that really has.

Possibly range? At that scale the max representable duration is about 16.5 years (assuming they're 64 bits, IIUC the standard mandates that as a minimum) which could be limiting - although that seems unlikely to be a concern in the framerate domain, but who knows what it might get used for when that might become an issue.

CLA?

Usually: contributor license agreement.

newp?

Diminuitive of 'nope' :)

Ahh like this: https://goo.gl/images/eRKmN4

Thanks.

The problem is that NTSC isn't 30Hz, it's 29.97Hz (or exactly 30/1.001Hz). This was due to some technical issues when introducing colour transmission, see https://en.wikipedia.org/wiki/NTSC#Lines_and_refresh_rate

I don't think you understand the comment you are replying to.

Yeah, I had a brainfade with reading comprehension. The OP is of course correct.

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