Perfect motion at 24 fps from 96fps

[Rui Guerra]

Hi all,

Following a post in another thread, it as been said that:


" If you shoot 96 fps and 1/96th of a second at 6K 2.4:1, then you can combine two frames and drop two frames to create 24 fps at 1/48th of a second for perfect motion and you can still choose whatever still frame works for you (with a 1/96th shutter speed and 6144x2592 image size). Shooting 96 fps means you get approximately 24-40 frames per cheetah stride, two to four of which have a paw stopped on the ground.

If you really want to shoot 8K you need to drop your speeds to 48 fps and 1/48th of a second to get perfect motion (dropping every other frame)."



This is very interesting and from a mathematical point of view its obviously correct. That will solve the situations when weren't sure if the footage will be used in slow-motion or in real-life speed or if you want to do some speed-ramp in post.

From a practical perspective, how can this be done, in Redcine X, FCPX or Resolve?
I mean how can we choose the correct settings so the software knows that it should merge two consecutive frames and drop the next two and so on (in the example of converting an 96fps @ 1/96 into a 24fps @ 1/48) ?

Thanks,

 

[Michael Tiemann]

Turns out to be not that hard to do in Resolve. This project (which uses a 192 frame 24fps leader sequence I downloaded from the net) shows how it's done:

https://www.dropbox.com/sh/em4h69d4rzydw40/AADiBfSA3Zmj0pcuvltiScLGa?dl=0

In words: take the sequence you want to slow down, place it on a video track, duplicate it, and place the duplicate on a 2nd video track, offset by a single frame (plus 1 or minus 1 does not matter). You need to choose a composite mode. Lighter will preserve your whites, Darker will preserve your blacks, Add will give a sum, which can be cut in half using curves, but if there's a bright o dark flash, the average will look funny. Screen might also be a good choice. In any case, once you have a composite mode you like, make a compound clip of the two clips. You should now see adjacent frames blended together. That's the blending part. Then, set the clip speed to 400%. This will pick one (blended) frame and discard the next three, then pick another (blended) frame and discard the next three. Suddenly, you have 96fps original material playing back at 24 fps with the motion blur of 48 fps.

 

[Rui Guerra]

Hi Michael,

Thanks for the explanation, although I've tried to open the project in DaVinci but I get a "Media Offline", so can't see it.

 

[Michael Tiemann]

Hi Michael,

Thanks for the explanation, although I've tried to open the project in DaVinci but I get a "Media Offline", so can't see it.

Replace that clip with your own media and it should do what you expect.

 

[Karim D. Ghantous]

If there's a way to write scripts in Resolve, something like this could work? The core code should be primary school level simple. I'm using pseudocode because I don't know what the commands are. Line numbers are for reference:

10 VAR startingFrame
20 VAR totalFrameCount
25 REM totalFrameCount will be an internal variable given to each video clip by the application
30 for startingFrame = 1 to totalFrameCount
40 average (startingFrame, startingFrame+1)
50 startingFrame = startingFrame+3
60 next startingFrame

Programming is kind of fun. I wish I did more of it.

 

[Rui Guerra]

Karim's approach is interesting, although (I think) a little bit out of the scope of most of us as video guys (and not IT people).

Still didn't try replacing some media in the "conversion project" that Michael sent, but in the meantime, if someone have any other solution in Resolve or FCPX (preferably not using programming), it will be great to learn more than one way to achieve the same goal.

Thanks,

 

[David Rasberry]

Karim's approach is interesting, although (I think) a little bit out of the scope of most of us as video guys (and not IT people).

Still didn't try replacing some media in the "conversion project" that Michael sent, but in the meantime, if someone have any other solution in Resolve or FCPX (preferably not using programming), it will be great to learn more than one way to achieve the same goal.

Thanks,

Don't know about for Macs, but I use Acrovid Intertake for general transcoding utility functions on Windows. It can modify clip frame rates up or down, including interpolating new frames, and has a blur adjustment feature. Reads and writes most pro and consumer video codecs, including Prores, DNX HD/HR, Cineform DI formats. Does not work with raw codecs though.

http://acrovid.com