720 x 486 (640 x 480), what doe it mean exactly?

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720 x 486 (640 x 480), what doe it mean exactly?

ok so. i was running some tests with my decklink card and captured some footage with the bundled application deck control. i was capturing from a digi-beta deck at blackmagic 10 bit ntsc. when i go to open the clip it reads this in the frame size 720 x 486 (640 x 480) and seemed less wide and not stretched than when i capture with final cut and open the captured clip. it seemed to correspond with the way a 720 x 486 clips is displayed in an ntsc monitor. when i imported it into a final cut sequence at 10 bit 720 x 486 it looked fine and didnt ask me to render or change sequence to match clip. it also looks fine in my ntsc monitor.
so here's my theory.
quicktime is telling me that if the clip is displayed in a computer monitor it will display at 640 x 480 compensating for sq/nonsq pixel differences. and when it is outputed to a ntsc monitor it will display at 720 x 486.
i guess my questions are...
a) does anyone concur on this?
b) is this 720 x 486 (640 x 480) safe for broadcast?
c) i've gone in the exact opposite direction and i am completely wrong, aren't i?
sorry for the long post and thanks for all your help!

macbook pro

Posted on Dec 10, 2008 2:35 PM

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Answer 1

Dec 10, 2008 2:55 PM in response to ccid

I'd concur with your theory.

Most broadcasters would require 720x486 (standard for uncompressed 8 or 10 bit) as opposed to DV-NTSC, which is 720x480.

I think you're on the right track...is there an issue at hand?...like, when you 'captured with FCP', what capture settings did you use?..and how did you get it in, w/o using the Decklink?

K

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Answer 2

Dec 10, 2008 3:00 PM in response to Kevan D. Holdsworth

Most broadcasters would require 720x486 (standard for uncompressed 8 or 10 bit) as opposed to DV-NTSC, which is 720x480.,

except in those times when it's 640x480.

I don't get it.

bogiesan

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Answer 3

Dec 10, 2008 5:19 PM in response to David Bogie Chq-1

Yeah I don't get those figures either, PAL is 720x576 non-square or 768x576 square pixels. Surely NTSC must be 720x480 (or 486 if not dv) non-square and 768x480 square? No? Or is NTSCs pixel aspect different to PAL.

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Answer 4

Dec 11, 2008 9:30 AM in response to Jon Chappell

Thanks Nick and Jon. So, NTSC and PAL do indeed have different pixel aspect ratios, I guess I should have realised seeing as they have a different number of horizontal lines. In order to maintain a 4:3 aspect ratio the pixel aspect has to be different.

One little quibble, the Digital Rebellion site refers to PAL as being 720x540 square pixels. In theory I guess this makes sense but in practice PAL is always referred to as 768x576 square. This way, both NTSC and PAL do the math on the horizontal not the vertical.

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