Purpose of Effect of 3:2 Pulldown

[Mark Job]

Originally Posted by Adam Stanislav

I can only hope that we will eventually abandon this anomaly and go to true 24/30/25 fps in the digital world. The way we are doing it is a pain for those of us who write video editing software because sound continues to use Hz, or cycles per second, so keeping everything synchronized when you trim clips and move them around requires you to be aware of the different timing. It is not too difficult with the 24/1.001 video fps as you can think of 48 kHz as 48048 cycles per 1.01 second, so you have exactly 2002 sound samples per 24/1.001 fps video frame. But it does not workout as neatly with the 30/1.001 fps video where you have exactly 8008 sound samples per 5 video frames. And it gets even more complicated with 25/1.001 fps, where you are perfectly synchronized only once every 25 frames. That is another good reason to shoot at 24/1.001 fps as opposed to 30/1.001 or 25/1.001 fps.

...Dear Adam & Dan: I can see allot of very serious drinking went into this rigged up fixing of the video signals ! I sincerely wish they would make cameras and VTR's & TV's do *True fps speeds whatever they are. i.e. 24 or 30 or 60 fps. I think we're at the age now in digital video when we can do away with the rounded off 23.976 and 23.98, or 29.970.

[Aaron Newsome]

Originally Posted by Luben Izov

Anything shot in North America digitally that refer to 24p is 23.976fps. AVID call that 23.98fps, some call it 23.97, but it is only 23.976 and that is true 24p in North American terms because of TV frequency standards. Hope that helps.
Cheers
;-)

That's incorrect Luben. My camera is digital and it shoots 24fps and 23.98fps (23.976). If I need a real true 24fps, then I select that. Pretty sure mine isn't the only camera that does this.

[Billy Steinberg]

Originally Posted by Adam Stanislav

If I recall correctly, way back when the old B&W TV aired at 30 fps (60 fields/s) in North America and 25 fps (50 fields/s) in Europe. When color was added, they wanted to be backwards compatible with the existing B&W receivers, so they did two changes.

Well, more than two changes, but so far so good.

(1) They continued airing the B&W signal and added the color difference (as is still done in many digital codes, such as the various MPEG standards).

Well, the concept is correct, and they certainly did what they did to maintain compatibility with all the black and white tv's, but that's not how color was encoded. You're thinking in the current scheme of things, but back then the color was added via a color subcarrier, making what is called a composite video signal. The NTSC color subcarrier was at 3.58MHz, and the PAL subcarrier was at 4.43MHz. The component encoding system, which does indeed use color difference (R-Y, B-Y) is something else entirely, and is in common use today. Pretty much all digital schemes use component (color difference) now.

(2) They slowed down the fps by 1.001, so it became 30000/1001 in North America and 25000/1001 in Europe. They did that so they could fit all the additional color information into the existing bandwidth.

Umm, no on both counts. PAL was never involved with the 1000/1001 stuff; its frame rate in the analog days was 50.00 as it still is today. And the reason for the frequency change in NTSC land was to avoid interference between the 3.58MHz chroma subcarrier and the 4.5MHz broadcast sound carrier; it had nothing to do with fitting the new color info into the channel bandwidth.

We are still stuck with this anomaly because when we switched to all digital TV, they still wanted to stay compatible with all the analog TV sets (with just a converter box added) that people owned or perhaps still do.

I should just give you this one :), but arguably, this was due to standards committee politics; many of us felt it was time to give up the stupid, no longer necessary, 1000/1001 stuff. There is no need for it technically, including converter boxes.

I can only hope that we will eventually abandon this anomaly and go to true 24/30/25 fps in the digital world. The way we are doing it is a pain for those of us who write video editing software because sound continues to use Hz, or cycles per second, so keeping everything synchronized when you trim clips and move them around requires you to be aware of the different timing. It is not too difficult with the 24/1.001 video fps as you can think of 48 kHz as 48048 cycles per 1.01 second, so you have exactly 2002 sound samples per 24/1.001 fps video frame. But it does not workout as neatly with the 30/1.001 fps video where you have exactly 8008 sound samples per 5 video frames. And it gets even more complicated with 25/1.001 fps, where you are perfectly synchronized only once every 25 frames. That is another good reason to shoot at 24/1.001 fps as opposed to 30/1.001 or 25/1.001 fps.

I don't question the difficulties and extra work you have to go through, and I wouldn't mind not having to say 29.97 or 23.976 ever again, particularly since there is really no technical need for the 1000/1001 stuff anymore, but I do wonder where you're getting "25/1.001 fps" footage...

Billy

ps For those that want to learn more (or check to see if I just made this all up), click here for a little that Wikipedia has to say on the subject of frame rate.

[Luben Izov]

Thank you for correcting me Aaron! I just didn't wanna go to any further complications then what we are in all ready ;-). The fact that some cameras can shoot 24p would make the 23.976 even more complicated for explanation and understanding. I personally don't wanna elaborate on that. Although, today's kids from film school don't understand why 23.976fps. I go trough this routine in a daily bases with volunteering students trying to get the truth on set after they learn something from someone who never was on set or in Post before. I would guess that you probably had that experience yourself ;-)
Regarding the 25fps - their is no complication in Europe.
Cheers

[Adam Stanislav]

Originally Posted by Dan Keaton

Dear Adam,

As far as I know, 25 is true in the digital world, as 50i is also true.

Originally Posted by Billy Steinberg

PAL was never involved with the 1000/1001 stuff; its frame rate in the analog days was 50.00 as it still is today.

Thanks for clearing that up, guys. That is very good to hear. Also, thanks, Billy, for the details for the reasons for it all.

[Daniel Symmes]

Actually, as I recall for my misspent youth, the off numbers come from a frequency shift needed to prevent the color encoding from interfering with the audio.