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Shooting 21fps for action


Max Field

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Could someone please lay out samples or a graph or something similar of the 21fps shooting phenomenon?

I've seen a few behind the scenes clips where a glimpse of the monitor shows they're recording in 21fps and to my understanding this is supposed to make the motion slightly snappier?

How does this playback different from shooting 24fps and slightly speeding it up? Or they keep it at the same right just to make it a little choppier?
When 24fps is played back into 30fps there's a 2/3 pulldown, is there a pulldown equation for 21fps into a 24fps project?

Thanks for the science on it.

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It is quite difficult to get smooth motion by speeding up 24fps originals to play back as if it were shot at 21 fps.  To do this, one must eliminate 3 frames every second.  And those missing frames will show an obvious jump of action.  There are frame blending techniques in post to try to smooth this out, but it doesn't always look good.

Shooting a 21fps original means that there will be equal time between each frame/exposure and the motion will play back smoothly, although it's still possible that viewers will perceive the cheat and the effect can look fake.  Our brains are very sensitive to the look of gravity and "fast motion" capture can hit us as fake, depending on the type of action.

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The Fast & Furious franchise is a great example of undercranking the action scenes. We shot these fight scenes and action driving sequences at 22 FPS at a 90 degree shutter. That combo really works!

G

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11 hours ago, Gregory Irwin said:

The Fast & Furious franchise is a great example of undercranking the action scenes. We shot these fight scenes and action driving sequences at 22 FPS at a 90 degree shutter. That combo really works!

Greg,

You're narrowing the shutter to get motion blur that would normally be associated with the faster frame rate, correct? I'm surprised that you would go as far as 90 degrees since you're only slowing down the camera speed by 2 frames, but perhaps with trial-and-error that's what looked best?

Also, years ago a colleague who worked on the Fast N Furious movies told me that in the driving scenes, the cars are only going 40mph because of safety rules. Is that true? You guys must shoot a lot of undercranked scenes!

- Webster

 

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1 hour ago, Webster C said:

Greg,

You're narrowing the shutter to get motion blur that would normally be associated with the faster frame rate, correct? I'm surprised that you would go as far as 90 degrees since you're only slowing down the camera speed by 2 frames, but perhaps with trial-and-error that's what looked best?

Also, years ago a colleague who worked on the Fast N Furious movies told me that in the driving scenes, the cars are only going 40mph because of safety rules. Is that true? You guys must shoot a lot of undercranked scenes!

- Webster

 

Hi Webster,

Remember, a normal shutter is 180 deg. By shortening the shutter, you are eliminating motion blur and making each image sharper. In musical terms, the footage looks more staccato. By shooting the 90 deg shutter in combination with the 22 FPS, you add edginess to the movie. It looks great! 
I don’t believe your friend about the 40 mph. Over the five FF pictures I worked on, we had stunt drivers driving on the edge. 

 

G

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  • 11 months later...

Sorry to bump but was still looking for a visual or demonstrative sample of inserting a 21fps clip into a 24fps timeline (Youtube has next to nothing).

If the camera doesn't have a project framerate setting but you have a 21fps file, when drug into the timeline does it slightly speed up or just get under sampled? Or is there an entirely different workflow I should be mindful of?

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1 hour ago, Phil Rhodes said:

Another good trick is just to manually cut out a frame here or there to speed up moments of impact in fight scenes. I can't find an example but I've done this and made stuff that looked limp on the day look pretty decent in the end.

Monty Python did that for some brutal hits in "Holly Grail" and "Life of Brian".

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15 hours ago, Phil Rhodes said:

Another good trick is just to manually cut out a frame here or there to speed up moments of impact in fight scenes. I can't find an example but I've done this and made stuff that looked limp on the day look pretty decent in the end.

IIRC this was done in Blade Runner in the scene where Leon Kowalski confronts Deckard. Specifically, when Kowalski smacks the gun out of Deckard's hand.

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On 9/30/2020 at 7:56 AM, Max Field said:

Sorry to bump but was still looking for a visual or demonstrative sample of inserting a 21fps clip into a 24fps timeline (Youtube has next to nothing).

If the camera doesn't have a project framerate setting but you have a 21fps file, when drug into the timeline does it slightly speed up or just get under sampled? Or is there an entirely different workflow I should be mindful of?

I believe the answer that you're looking for is that a scene is captured at 21fps and then when edited, it's played back at 24fps and thus makes all the action look like it's occurring faster. 

In today's digital editing environment when you capture a file at 21fps, yes the file itself is encoded to play back at 21fps. But what you do is bring it into your editing program and "interpret" the footage as 24fps. What that does is tell the computer "hey, make sure you play back this specific file at 24fps" and therefore you have your fast motion look. 

This "interpret footage" procedure is very common for editors and can be done with pretty much any file. I do this with 60fps files all the time.

If you were to do nothing and just drag it into a time line as you suggested.... Let's say it's a 24fps timeline.... The computer will duplicate some frames in order to get it to conform to 24fps, this is usually never desirable. 

Alternatively there are some cameras now-a-days that can do all of this for you in camera. For example on the gh5, there is a mode called "variable frame rate" and what that does is capture your scene at whatever fps you tell it to, but then it automatically encodes it to play back at 24fps (or 25 or 60 or whatever) which is a nice feature. 

This is pretty much the same thing as what's present in the Alexa with what you mentioned as the "project frame rate" 

Hope that helps! 

 

 

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