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Need Assistance With Strobing Edges On Speed Changes

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David BeardNeed Assistance With Strobing Edges On Speed Changes
by on Jan 20, 2012 at 1:43:54 am

Hi there, I'm hoping someone can offer up some help on how to fight this issue I'm having. So I'm working with some RED One footage. I have this one shot that is a dolly move from right to left, shot at 48fps, 1/120 shutter, in a 23.976 time base. The clip is fine as shot, but the client would like me to speed it up so the image matches the script a little better. When I attempt to speed this clip up, the edges of the apples start to strobe. Is there anything I can do to smooth this out in AE? Here is a sample.


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Dave LaRondeRe: Need Assistance With Strobing Edges On Speed Changes
by on Jan 23, 2012 at 9:35:43 pm

There may not be much you CAN do. You're seeing a phenomenon known as Judder, where the viewer sees horizontal motion as a series of herky-jerky images.

It's a function of both horizontal speed and frame rate, and it becomes more commonplace at lower frame rates... like 23.976.

Now you said it was SHOT at 48fps. Did you really MEAN 48fps, or 23.976*2, which would be 47.952? If the footage reads 48fps in AE, try conforming it to 47.952 in the interpret footage settings, and then playing around with the speed.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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David BeardRe: Need Assistance With Strobing Edges On Speed Changes
by on Jan 23, 2012 at 9:41:12 pm

I think it's for sure judder after to speaking with a few more experienced people then myself. The footage was shot in a 23.976 time base on a RED One at 48fps, so I overcranked. The footage shows up as 23.976 in REDCine-X Pro.


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Dave LaRondeRe: Need Assistance With Strobing Edges On Speed Changes
by on Jan 23, 2012 at 9:46:56 pm

I'm unsure what you mean by, "shot in a 23.976 time base on a RED One at 48fps". Does this mean the shutter speed was 1/48 sec?

Depending on what the client wants, the problem may call for a re-shoot. If you have access to either Magic Bullet or Twixtor, you can change the speed of the footage without image degradation. AE all by itself isn't stellar at such things.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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David BeardRe: Need Assistance With Strobing Edges On Speed Changes
by on Jan 23, 2012 at 9:53:16 pm

In the camera, you have an option of what time base you're project will be. So, I can choose 23.976, 24, 25, 29.97, 30, 59.94, and 60. I think that's all of them. Then, you need to choose what frame rate you'll be shooting. Most of the time, we are shooting 24 fps, with a 1/48th shutter. You have the option to activate varispeed. This shot was 48fps, 1/96th shutter, in a 23.976 time base, which means, this shot, to the editor, is a 23.976 clip, with slower motion. I have been doing some experimentation in Twixtor, and I'm getting slightly better results.


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Dave LaRondeRe: Need Assistance With Strobing Edges On Speed Changes
by on Jan 23, 2012 at 9:57:32 pm

AE may not have access to all that metadata. Double-check the footage's frame rate in AE's Interpret Footage settings.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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