23.98p or 24p?

Jeff Troiano

Jeff Troiano

23.98p or 24p?

Was going to write a big long question, but the long and short, when do I use one over the other?

Have search the web, read some older forum post and articles. I understand the history behind 23.98 and 29.97.

I'm just still a bit foggy on when I would want to use one over the other.

Thanks,
Jeff
 
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If I'm reading what I'm finding on the web correctly, if I am delivering for NTSC broadcast TV, I'd want to shoot in 23.98. But since I'm pretty much filming for YouTube or web delivery, I'm good at 24p.

Waiting for the audio guys to chime in. Thought there was an audio sync issue that could arise when using one over the other. But can't remember what it was I read.
 
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I'm counting the minutes until one of IT's more technically-adept step in and really answer the question. This one has always seemed weird to me.

For a long time, I thought that 24 was just a short-hand way of saying 23.978. Because who the F actually uses TRUE 24p? What purpose does that serve?

But then I experienced a couple headaches when unwittingly exporting a project to TRUE 24p. Having been filmed in 23.978, and with audio people expecting 23.978, TRUE 24p proved to be like throwing a wrench in the system.

I emphasize "TRUE" 24p because I've definitely experienced more than one example of a company (either a camera manufacturer or NLE company using the term "24p" to actually mean "23.978". It's annoying, you gotta read fine print and specs.

I'd also like to know when the heck anyone would choose true 24p. Cuz every single application I know of requires 23.978.
 
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The difference is actually quite simple, although it's tricky to explain simply. :)

24fps is called film speed and is used specifically for film (35mm film and DCP) whereas 23.976fps (often incorrectly annotated as 23.98fps) and 29.97fps are video speed. In practice, you cannot have .976 (or .97) of a frame! 23.976fps is actually 24fps recorded slightly (roughly 0.1%) slow. In other words, at 23.976fps or 29.97fps the time-code does NOT equal actual time. It's for this reason that drop frame (DF) was invented, where 2 frame numbers are dropped every minute (except for each 10th minute), so the time-code would agree with actual time, which would otherwise be a nightmare for those having to work out TV broadcast schedules.

None of this is a problem most of the time and you can pretty much ignore the whole thing. A problem only arises when converting between film speed and video speed. Let's say you shoot at 23.976fps and then decide to convert to 24pfs (for say a DCP), now you're running your film at film speed but your production sound was recorded in time with the picture running at video speed and will drift noticeably now your picture is running at a faster speed. Obviously the reverse is also true, if you shoot at film speed and then convert to video speed your production audio will drift by the same amount but in the opposite direction because your picture is now running 0.1% slower than your audio (rather than 0.1% faster). The obvious solution is not to convert your picture, shoot and edit at the speed you intend to distribute. There are various production sound/post prod sound workflows which can account for a film which needs to be distributed at a different speed to what it was shot or edited at. You may have seen somewhere in your NLE audio settings called Pull-Up and Pull-down rates? These settings are specifically part of these workflows but how you use these pull-up/down rates needs to be worked out before you start shooting your film.

G
 
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As far as I'm aware all commonly available digital video cameras that shoot "24p" are actually shooting at 23.976, so that's what you should be using throughout your post process. Only exception I can remember is the 5DmkII, which initially shot a true 30p that caused all kinds of sync problems with dual system audio - but they fixed that in firmware.
 
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Was curious because My new camera listed frame rates as 23.98p, 24p, 25p, 29.97p, and 30p

I was,wanted to know when I'd use one over the other.

And ItDonnedOnMe, I think you hit on what I had remembered reading. That using dual video/audio systems, the audio would not sync up properly when true 24p or 30p was used. Again, I don't know this to be fact, just trying to remember what I had read.
 
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Jeff Troiano said:
... using dual video/audio systems, the audio would not sync up properly when true 24p or 30p was used. Again, I don't know this to be fact, just trying to remember what I had read.
Click to expand...

Obviously my explanation was not very clear! 23.976fps is actually 24fps, what changes is the length of the time-code second because you effectively slow down 24fps by roughly 0.1% to arrive at a frame rate of 23.976. The same is true with the relationship between 29.97fps and 30fps. These two slowed down frame rates (23.976 and 29.97) are called video speed.

If you are recording production sound on a separate recorder it doesn't matter whether you are using film speed (24fps) or video speed, the dialogue will sync properly. The problem arises when you convert your picture between film speed and video speed. Your converted picture will run slower or faster than your production sound and you will not achieve sync. Your NLE could also cause a problem, FCP7 has a nasty bug between film speed and video speed when importing audio.

The only time you would use 24fps (film speed) is when your final output will be to DCP or 35mm film, otherwise stick to 23.976fps for HD (TV or Bluray) and 29.97fps for SD (TV or DVD). BTW, because both 23.976 and 29.97 are both video speed, you should be able to convert between the two without loosing sync with your audio. It's only when going from video speed to film speed (or vice versa) where you are going to run into a problem.

Hopefully this is a bit clearer?

G
 
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Jeff Troiano said:
Thanks APE, crystal clear now.
Click to expand...

No problem. A number of years ago when I used to teach this stuff, I always had difficulties explaining this topic and therefore I always had some students who couldn't get it. The situation now is actually quite a bit easier than it used to be; in the 90's it was common for 35mm films to be converted to video speed for editing and then converted back to film speed for printing/distribution. It required very careful workflow planning to avoid disasters!

BTW, I didn't mention 25fps because you won't need to consider it, unless you are thinking about international TV sales/syndication. 25fps is PAL (or SECAM), which is the SD broadcast standard in much of Europe, Brazil and a number of other countries, the US uses NTSC (29.97fps) for SD broadcast. If you have ever come across pull up/down rates of 4% (rather than 0.1%) in your NLE, these settings are used to convert between film speed and PAL.

G
 
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What APE said ^

It just reminds me of the issue of standardization. People say give film more time since it is a new medium compared to the other arts but they do not take into the account that we've been progressing exponentially and not in a linear fashion.

Frame rates are the least of it. We can not figure out a way where a film will look the same in a theater, on a DVD and on a TV. An experience provided by film which is fully thought out is not the same depending on where and how you watch it.

Smooth out that motion blur for me, please :rolleyes:
 
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23.98 is pseudo 24 on a 60i timeline. It's interlaced analog NTSC all the way.

Personally, I'm shooting in true 24p with a slow shutter. When I export from FCPX into a Pro Res 422 HQ file (.MOV - Quicktime container for H.264), it's framerate will actually say 24, just like a progressive Blu-ray. Perfect for converting to film at a later date.

I always stay away from any interlaced formats. What is this, the 1970s? hehe
 
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Loud Orange Cat said:
23.98 is pseudo 24 on a 60i timeline. It's interlaced analog NTSC all the way.
Click to expand...

Not necessarily. 23.98 is just a playback rate, and while it was originally adopted to help fit film originated footage into a 60i (actually 59.94i) video stream that doesn't make it pseudo 24 or interlaced (or analog for that matter).

Higher-end prosumer cameras that shoot true "24p" actually most commonly do so at 23.98. It's still a progressive format, no interlacing. Lower end cameras tend to do the 24-in-60i thing, probably for widest compatibility with consumer televisions. If you're planning to do anything serious with your footage you definitely want the former.

Personally, I'm shooting in true 24p with a slow shutter.
Click to expand...

That seems kind of odd. What camera is this? When you say slow shutter, how slow do you mean?
 
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ItDonnedOnMe said:
That seems kind of odd. What camera is this? When you say slow shutter, how slow do you mean?
Click to expand...

I'm shooting with a Canon Vixia HF G20. It has four shooting modes: 60p (both fields replicated twice), 30pf (30fps interlaced on 60i timeline), 24pf (24fps interlaced on 60i timeline) and 24F (true 24fps with slow shutter).

Canon's "slow shutter" mode leaves the shutter open for the 24th of a second instead of a 30th and any weird pull down conversion happens. For a small prosumer camera, it's pretty nice and the 24F footage looks incredibly like 24fps film with the slow shutter.

I was considering shooting 30 second examples in all four formats so everyone can judge for themselves. Should I?
 
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I believe on that camera the 24F mode is actually 23.98fps and progressive.

The slow shutter is an odd choice. Standard film shutter speed would be 1/48th (180 degree shutter), 1/24th isn't actually physically possible on a film camera. Running your camera at 1/24th will tend to make the motion look more video-like despite the 24 frame rate. When you see an odd video-look shot in the middle of a film like "Apocalypto" that's because they used too slow of a shutter. If you're trying to get the classic 24 frame film look you should actually turn the slow shutter off.
 
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