Jump to content




Photo

why 23.976 and not 24 fps??

frames

  • Please log in to reply
10 replies to this topic

#1 davide sorasio

davide sorasio
  • Basic Members
  • PipPip
  • 89 posts
  • Student
  • New York

Posted 02 May 2016 - 09:22 AM

why 23.976 and not 24 fps? And when should I set the camera and the monitoring out option for the BNC for one or the other?


  • 0




#2 Landon D. Parks

Landon D. Parks
  • Basic Members
  • PipPipPipPip
  • 1627 posts
  • Producer
  • Cincinnati, Ohio

Posted 02 May 2016 - 09:55 AM

23.976 is still 24 progressive frame. 23.976 is really a hardback to the old NTSC standards adopted in the early days of television. Has something to do with timecode and compatibility with older broadcast systems. In a modern sense, you can shoot either frame rate. Just keep in mind that you want to shoot the SAME frame-rate across the project. If one camera shoots 24 and the other 23.976 you'll have a harder time matching them. 

 

I'd say as long as all your camera's and project files will be 24.00, the shoot at 24.00. That is DCI spec, and if anything needs to be delivered 23.976 (would that even happen?), it can be done in post. 24 even frames per second just seems more 'fluid' to me.


Edited by Landon D. Parks, 02 May 2016 - 09:57 AM.

  • 0

#3 Stuart Brereton

Stuart Brereton
  • Basic Members
  • PipPipPipPip
  • 2575 posts
  • Cinematographer
  • Los Angeles

Posted 02 May 2016 - 10:02 AM

23.976 is a TV frame rate. 24fps only exists in cinema. If you're shooting for a TV finish use 23.976.


  • 0

#4 Perry Paolantonio

Perry Paolantonio
  • Basic Members
  • PipPipPipPip
  • 349 posts
  • Other
  • Boston, MA

Posted 02 May 2016 - 10:16 AM

I'd say as long as all your camera's and project files will be 24.00, the shoot at 24.00. That is DCI spec, and if anything needs to be delivered 23.976 (would that even happen?), it can be done in post. 24 even frames per second just seems more 'fluid' to me.

 

The right way to approach this is to work backwards from the deliverables format. If it's DCP, then 24. If it's broadcast, or if you want to make a DVD, then 23.976. 23.976 exists because it's the only way to encapsulate a 24fps progressive image inside a 29.97 interlaced package (NTSC), which is done using 3:2 pulldown. This pulldown can be undone if the cadence isn't broken, and a progressive image displayed even if it exists inside an interlaced stream. This is how it works on DVD, and on 1080i (in most cases). 

 

We usually recommend 23.976 because it's easier to get to more formats from there (NTSC, Progressive DVD, Progressive Blu-ray, 25fps). Changing to 24fps isn't particularly hard, but most of the common delivery formats work natively with 23.976, and only a couple (DCP, Blu-ray) support hard 24fps. And Blu-ray also supports 23.976


  • 0

#5 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 18789 posts
  • Cinematographer
  • Los Angeles

Posted 02 May 2016 - 10:18 AM

Truth is that most digital projects shot for either broadcast or cinema use 23.976 instead of 24 in the U.S.

 

It's nothing to do with timecode.

 

From Wikipedia on NTSC:

In January 1950, the Committee was reconstituted to standardize color television. In December 1953, it unanimously approved what is now called the NTSC color television standard (later defined as RS-170a). The "compatible color" standard retained full backward compatibility with existing black-and-white television sets. Color information was added to the black-and-white image by introducing a color subcarrier of precisely 3.579545 MHz (nominally 3.58 MHz). The precise frequency was chosen so that horizontal line-rate modulation components of the chrominance signal would fall exactly in between the horizontal line-rate modulation components of the luminance signal, thereby enabling the chrominance signal to be filtered out of the luminance signal with minor degradation of the luminance signal. Due to limitations of frequency divider circuits at the time the color standard was promulgated, the color subcarrier frequency was constructed as composite frequency assembled from small integers, in this case 5×7×9/(8×11) MHz.[7] The horizontal line rate was reduced to approximately 15,734 lines per second (3.579545×2/455 MHz) from 15,750 lines per second, and the frame rate was reduced to approximately 29.970 frames per second (the horizontal line rate divided by 525 lines/frame) from 30 frames per second. These changes amounted to 0.1 percent and were readily tolerated by existing television receivers.

 

So analog color NTSC runs at 29.97 fps / 59.94i.  This frame rate has been carried over into digital HD broadcasting in the U.S.

 

So throughout the 2000's, the main reason you shot at 23.976 fps instead of 24P was audio post in the U.S.  Even movies shot at true 24 fps had to deal with this because a telecine transfer to NTSC for dailies and NLE post changed the frame rate to 23.976 fps, so the frame rate didn't get restored to 24 fps until the movie was finished to film and projected at 24 fps.  So after a movie was edited offline, tape copies were sent to sound post for cutting and mixing sound, so they were working with material running at 23.976 fps whether or not it was shot at 24 fps or 23.976 fps.  If the final product was for broadcast, it didn't matter because it was going to get shown at 59.94i with a 3:2 pulldown anyway.  But for material destined for theatrical projection, at some point before or after the final mix (depending probably on whether they were mixing to a video copy or a print), the speed had to be corrected back to 24 fps.

 

So it because easier for digital projects to just shoot at 23.976 fps instead of 24 fps so that the sound post could stay at 23.976 fps all the way to the mix, after which one could decide if one needed a true 24 fps version.

 

Now that most sound people get digital files instead of tape copies of the offline cut to work from, it would be possible to eliminate dealing with 23.976 and stay at true 24 all the way through post, but it's been hard to change the industry, especially since so much post work is still done for television broadcast compared to for theatrical release.

 

My own experience shooting one of the first 24P movies in 2000 was that since it was for theatrical, I chose 24 instead of 23.976 in the camera menu.  Later when I asked the editor how the sound mix was going, she said "fine, except that the entire reels are drifting slightly out of sync and I'm having to manually adjust them."  Live and learn... this was probably the first 24P HD feature ever posted in Los Angeles at the time.  Ever since then, I've stuck with 23.976 for digital features and haven't had a problem.  But I think one could choose true 24 fps today and make it work.

 

As Landon says, DCI requires true 24 so digital movies shot and finished at 23.976 get converted to 24 for the theatrical DCP.


  • 0

#6 Landon D. Parks

Landon D. Parks
  • Basic Members
  • PipPipPipPip
  • 1627 posts
  • Producer
  • Cincinnati, Ohio

Posted 02 May 2016 - 10:39 AM

Ah, I was not aware that 23.976 was still needed for digital broadcast. I guess I just like the idea of shooting 24p rather than an off frame rate. Film has been shot that way for over a hundred years. That is not to say you should take my advice and shot 24 progressive (some camera's don't even offer it as an option), but that is the way I shoot on my GH4 and have had no problem with DVD output. I also record sound in-camera rather than separate, so that whole sync-issue really doesn't exist in my workflow.

 

As others have said, most people shoot 23.976, and doing so will not be detrimental to your workflow. Just keep in mind that if you ever plan to do a DCP (lots of major festivals are moving toward this now), you'll need to have a 24.00 progressive JPEG2000 sequence. 


  • 0

#7 Brian Drysdale

Brian Drysdale
  • Basic Members
  • PipPipPipPip
  • 4745 posts
  • Cinematographer

Posted 02 May 2016 - 11:17 AM

The camera may even be running at 23.976, even though it says 24 fps on the camera (takes less space).


  • 0

#8 Perry Paolantonio

Perry Paolantonio
  • Basic Members
  • PipPipPipPip
  • 349 posts
  • Other
  • Boston, MA

Posted 02 May 2016 - 11:29 AM

The camera may even be running at 23.976, even though it says 24 fps on the camera (takes less space).

 

No it doesn't. It just plays at a different speed. Every frame is the same size.


  • 0

#9 Landon D. Parks

Landon D. Parks
  • Basic Members
  • PipPipPipPip
  • 1627 posts
  • Producer
  • Cincinnati, Ohio

Posted 02 May 2016 - 11:47 AM

 

No it doesn't. It just plays at a different speed. Every frame is the same size.

 

I think Brian is referring to the camera manufacturers naming 23.976p as '24p' or '24f' on their cameras. I don't know how common this is now, but back when there was no real cameras shooting TRUE 24P, 24P was still often used in the menu's and on literature to refer to 23.976.


Edited by Landon D. Parks, 02 May 2016 - 11:47 AM.

  • 0

#10 Perry Paolantonio

Perry Paolantonio
  • Basic Members
  • PipPipPipPip
  • 349 posts
  • Other
  • Boston, MA

Posted 02 May 2016 - 11:51 AM

 

I think Brian is referring to the camera manufacturers naming 23.976p as '24p' or '24f' on their cameras. I don't know how common this is now, but back when there was no real cameras shooting TRUE 24P, 24P was still often used in the menu's and on literature to refer to 23.976.

 

Ahh, ok. That makes sense!

 

Usually 23.976 is abbreviated as 23.98 (but they're not the same thing, and on long form material, that extra .004 makes a difference for audio sync!). Since we primarily deal with film and with tapes that have already been made, I'm not too familiar with how the camera manufacturers do that. If they're really abbreviating 23.976 as 24, that seems like a really bad idea!


  • 0

#11 David Mullen ASC

David Mullen ASC
  • Sustaining Members
  • 18789 posts
  • Cinematographer
  • Los Angeles

Posted 02 May 2016 - 12:43 PM

Yes, anyone shooting video on a still camera has to do some research to find out if "24" in the menu actually means 23.976.


  • 0



Also tagged with one or more of these keywords: frames

Ritter Battery

Technodolly

Rig Wheels Passport

CineTape

The Slider

Paralinx LLC

CineLab

Zylight

Glidecam

rebotnix Technologies

Aerial Filmworks

Pro 8mm

Tai Audio

Broadcast Solutions Inc

Abel Cine

Willys Widgets

Visual Products

Glidecam

Rig Wheels Passport

Pro 8mm

CineLab

CineTape

Technodolly

Tai Audio

Broadcast Solutions Inc

The Slider

rebotnix Technologies

Zylight

Visual Products

Willys Widgets

Aerial Filmworks

Abel Cine

Paralinx LLC

Ritter Battery