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24fps shooting vs. 23.976


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#1 Trevor McClung

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Posted 28 April 2012 - 04:24 PM

What is the difference? When a NLE system reads 24 fps does it mean 23.976? Or vise versa? Do I need a crystal synch motor to do both 24fps and 23.976? Is one or the other best for the 2:3 pull down or something like that? Help, please I'm about to pick the speeds to order on my crystal synch motor.
Thanks
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#2 Eugene Lehnert

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Posted 02 May 2012 - 09:48 AM

You will shoot true 24fps when you film. When you do the transfer on the telecine to tape/and or file, it will be slowed down to 23.976. The audio you shoot on set will have to be slowed by the same percentage to keep in sync with your picture. The post-house can do this for you. If you have the right audio recordist he can capture the audio at a higher sample rate so that when it's played back at 48khz the audio is at the correct speed.

You will edit at 23.976 in your NLE. HD cameras will nearly always be shooting video at 23.976. This frame-rate will convert to 29.97 SD or 59.94i HD using a 2-3 pulldown. If you had a true 24 signal it would convert into a 30 fps SD signal or a 60i HD signal. For video work you want 23.976. Then if you need to go film the HD master you create can be sped back up to 24p for a film-out or DCP.

People use 23.976 and 24p interchangeably though. So you might need clarification at times as to what someone really needs or is using.

The other catch is that your timeline will also not reflect time properly. If you think your film is 1-hour at 23.976 it's actually longer because you are playing your film slower than the 24 frame timecode. This is why drop-frame exists in SD. Timecode numbers are skipped at regular intervals so that the timecode stays accurate to length.

What is the difference? When a NLE system reads 24 fps does it mean 23.976? Or vise versa? Do I need a crystal synch motor to do both 24fps and 23.976? Is one or the other best for the 2:3 pull down or something like that? Help, please I'm about to pick the speeds to order on my crystal synch motor.
Thanks


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#3 Trevor McClung

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Posted 02 May 2012 - 10:36 AM

So it sounds like it would be best to shoot at the speed 23.976 on my Kinor 16? I can shoot 24 or 23.976 fps and 29.97 or 30 fps. I'm getting a crystal sync motor on Friday and must pick 6 speeds. I'm wondering if I should pick 23.976 and 24 as well as 29.97 and 30 fps? I had thought to pick 8, 12, 24, 30, 48, and 60 fps but now I wonder about 23.976.
The telecine house said 24 so now I'm a little confused.
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#4 Eugene Lehnert

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Posted 02 May 2012 - 10:53 AM

You should shoot true 24 on film. They are correct.

If you shoot at 23.976 it will be slowed down again when you transfer it to video.

Shoot true 24. Edit 23.976. Slow your on set audio down too.

Edited by Eugene Lehnert, 02 May 2012 - 10:58 AM.

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#5 Eugene Lehnert

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Posted 02 May 2012 - 11:05 AM

Thinking about it I might be incorrect. If you shoot 23.976 the telecine will actually play back the film at the proper speed it was shot at since it runs at 23.976. So therefore your audio would remain in sync. I've never tried this. Sorry for the confusion.
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#6 Matt Stevens

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Posted 02 May 2012 - 12:12 PM

How did we end up with such a confusing method?
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#7 Eugene Lehnert

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Posted 02 May 2012 - 01:03 PM

From what I understand television used to run at 30fps and when color was introduced tv was slowed down to 29.97fps to make room for the color signal and there lies the rub.

Japan has NTSC but they run their tv at 30fps and their analog black levels are at 0 IRE instead of 7.5 IRE that we have here in the states. We suffer because we had it all first. Maybe the internet will undo all of this one day.
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#8 Trevor McClung

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Posted 02 May 2012 - 01:46 PM

OK. They telecine house just said to shoot at 23.976 and 29.97 so now I'm going to be brave and eliminate 24 and 30 from the list of speeds to get on my camera. Or maybe I should get all four speeds to eliminate trouble in the future? The wise choice might be speeds 23.976, 24, 25, 29,97, 30 and 60? Should I get 8, 12, 48 or 60? I would use slo mo but probably not undercrank. Besides I could do fast speed on nle but slo mo suffers in nle so that answers that. What would be a better slo mo speed, 48 or 60? Probably 60 because I could always speed it up but it would take a bigger battery. Hmm I think I'm answering my own questions.
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#9 Jock Blakley

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Posted 02 May 2012 - 05:50 PM

True 24 would be advisable should you ever wish to contact-print for projection, as rare as that is nowadays.
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#10 Brian Drysdale

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Posted 03 May 2012 - 03:44 AM

Should I get 8, 12, 48 or 60? I would use slo mo but probably not undercrank. Besides I could do fast speed on nle but slo mo suffers in nle so that answers that. What would be a better slo mo speed, 48 or 60? Probably 60 because I could always speed it up but it would take a bigger battery.


I'd get 48 fps before having 8fps. I think I've used 18 fps more than anything below 12 fps.
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#11 Trevor McClung

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Posted 03 May 2012 - 01:28 PM

OK. Is the speed difference between 23.976 and 24fps noticeable? I think I have to shoot true 24 to insure the widest latitude of marketability. The only thing I don't know is what format it needs to be for TV. For instance, if I sell to HBO? Is that speed gonna be 23.976 converted to 29.97? Does 24fps have problems when converted to 29.97? I'm guessing not because of all of the movies on HBO. Maybe I'm reading to much into it and confusing myself but I need to know.

1. Are the movies on HBO running at a different speed than they were shot in?
2. What format do cable networks buy/broadcast, HD Tape, Digibeta, what?
3. Can someone confirm this procedure: shoot 24 then transfer to hard drive at 29.97, edit then export to tape for broadcast at 29.97 1080p???

Is that it?
Thanks guys.
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#12 Eugene Lehnert

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Posted 03 May 2012 - 04:47 PM

We here in the US run at 29.97 for broadcast. In SD it's referred to as 29.97 but in HD you see it as 1080i@59.94. The 29.97 number refers to frames and 59.94 refers to fields. Multiply 29.97 by 2 and you get 59.94 because there are two fields in one frame.

If you shoot 24 it will be slowed down to 23.976 for video. If you are making film prints from your negative there will be no speed change because projectors run at 24fps. If you shoot 23.976 on film, transfer it to video and finish in 1080p@23.976 and then transfer the video to film it will be sped back up to 24. HDCAMSR decks do this all the time. I can take a 23.976 tape and play it at 24fps or 25fps if I want. The speed change is minor and happens all the time.

The big issue is syncing external audio to your film transfers. They both need to run at the same speed to stay in sync. When you shoot 24fps on your camera the telecine slows the film to 23.976 so you have to slow your audio down by the same percentage. If you shoot 23.976 the telecine will play back the film at the speed you shot so there is no slow-down. In this instance the audio does not need to be adjusted to stay in sync with the picture. If you shoot 23.976 and try and sync audio up the audio on a film bench the audio will drift because the film is playing back at 24fps in the projector and it's now running faster then when it was recorded.

The usual workflow is: Shoot 24, transfer to 23.976 or 29.97, slow-down the audio, sync the audio, edit and output a 23.976 or 59.94 HD master. I would suggest creating a 23.976 master first and then adding the pull-down to create the 1080i@59.94 Drop-Frame broadcast tape. You just have to keep in mind that the timecode on a 23.976 timeline is not an accurate measure of time. Your film is actually running longer than what it is telling you.

I hope I haven't given you too much information to make it confusing.

Edited by Eugene Lehnert, 03 May 2012 - 04:49 PM.

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#13 Eugene Lehnert

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Posted 03 May 2012 - 05:20 PM

The digital stuff shot on HBO now originates at 23.976.
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#14 Mark Kenfield

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Posted 08 May 2012 - 07:52 AM

It's threads like this that make me really glad to live (and shoot) in PAL land.
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#15 Will Montgomery

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Posted 08 May 2012 - 11:03 AM

It's threads like this that make me really glad to live (and shoot) in PAL land.

You get used to it really quick.
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