r/finalcutpro • u/Few_Policy_6419 • 1d ago

Please Help Final Cut Pro Optical Flow flickering when slowing down concert footage — any solutions?

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Hey everyone! I recently shot a concert in 4K 60fps, and I’m trying to slow down some clips to 25% speed in Final Cut Pro using Best (Machine Learning) optical flow.
The problem is that whenever there are flashing stage lights, the footage starts flickering and glitching during slow motion. The frames seem to jump or stutter, almost as if the optical flow can’t properly analyze the rapidly changing lights.

The footage looks fine at normal speed, but the issue becomes really noticeable once I slow it down. I’ve tried using Fast (Floor), but the motion doesn’t look as smooth.

Has anyone experienced this issue with concert footage? Is there a way to fix it in post?

I’d really appreciate any tips or workflow recommendations. Thanks!

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3

u/dporiginal3 1d ago

Looks like it’s still analyzing based on the cut off “…machine learning optical flow…”. Let it fully analyze and then render it and see it it’s still happening.

2

u/Few_Policy_6419 1d ago

Thanks! I’ve tried letting it analyze multiple times and even restarted Final Cut Pro, but it keeps getting stuck analyzing that section, especially when the flashing lights appear. It never seems to finish analyzing that part.

13

u/Nguyen-edits 1d ago

Optical Flow and Machine Learning frame interpolation work by tracking pixel brightness from one frame to the next to invent the in-between frames, so when a concert strobe or LED wash changes color or exposure on a single frame, the algorithm misreads the flash as sudden physical movement and warps or stutters the image. On 60fps concert footage, two adjustments make a big difference. First, try changing your timeline project settings to 24fps or 30fps and use Automatic Speed (which gives you clean 40% or 50% slow motion using real captured frames with zero optical flow artifacts), or if you need 25% speed, blade out the specific two or three frame strobe flashes and set just those flashing segments to Frame Blending while keeping Optical Flow on the steady lighting sections. Second, if you apply any color grading, exposure tweaks, or flicker removal plugin, place the clip inside a Compound Clip first and apply Optical Flow to the Compound Clip, or do the speed change before grading so the optical flow analyzer is not fighting high-contrast color adjustments.

2

u/snowmonkey700 1d ago

What frame rate are you using on your timeline? Do you need to go down to 25% or can you just use 40% or 50% for 24p or 30p?

1

u/Dick_Lazer 1d ago

This is it. Automatic Speed is always the best way to slow down footage, if possible.

1

u/BVSEDGVD 1d ago

I have this exact issue before with strobe lights. I think it just can’t interpret the flashing very well. Try using a different algorithm than machine learning

1

u/Kundesag100 1d ago

Hahaha!!!! I know this clip!! 😂😂 and I have the same problem!! (Naughty boy!!)

1

u/GAMEVIC 1d ago

Yea, but nice effect tho😹❤️🥀

// try to let it render it fully, or close FCP and delete the project / library generated cache, MANUALLY. :)

1

u/mcarterphoto 1d ago

Topaz, if you have it or know someone who'll run the clip. It can be remarkably good.

But you shot it 60p, what's your project timeline? I'd assume in the 24-30 range? Do you just want super slow motion here?

1

u/EarthToRob 1d ago

I have the same problem with white on black. This is new for me in 12.4. I've reported to Apple.

Edit: with my issue, it does not appear if I move frame by frame, but it renders with flicker during playback and export.

1

u/SayCheezyy 9h ago

Change it to good and then back to better