Even Frames

Repairs the stutter in AI-generated video. Free, open source, Windows and macOS. You do not need to know how to code.

Clips out of Seedance, Kling, Veo, Runway, Hailuo and the rest very often do not run at an even 24 frames a second, even though the file says they do. Something in the generation or the export threw a frame away, or repeated one, or squeezed a 30 fps render onto a 24 fps grid. You see it as a hitch about once a second. On a timeline next to clean footage it is the first thing anyone notices.

This fixes it. Drag the file on, wait, get a repaired file back.

    <your clip>.mp4  ->  <your clip>_even.mp4

The result is always 24 fps, always the same number of frames, and always the same duration as the original. It drops straight back onto your timeline and the audio still fits. If a clip cannot be repaired under that rule, the tool says so and leaves your file alone.

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Install

You need two free programs: Python and ffmpeg. Neither has a window; they run behind the scenes.

Windows

winget install Gyan.FFmpeg
winget install Python.Python.3.12

Then close that window, open a new one, and double-click 0-SETUP-CHECK.bat.

macOS

brew install ffmpeg python

Then double-click 0-SETUP-CHECK.command. If macOS refuses to open it, see READ-ME-FIRST-MAC.txt — one right-click gets past it.

READ-ME-FIRST-WINDOWS.txt and READ-ME-FIRST-MAC.txt walk through all of this slowly, with nothing assumed.

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Use

	Windows	macOS
Is everything installed?	0-SETUP-CHECK.bat	0-SETUP-CHECK.command
Fix a clip	1-FIX-VIDEO.bat	1-FIX-VIDEO.command
Just tell me what is wrong	2-DIAGNOSE-ONLY.bat	2-DIAGNOSE-ONLY.command
Does the repair still fit the audio?	4-CHECK-TIMING.bat	4-CHECK-TIMING.command
Do the tools themselves still work?	5-SELF-TEST.bat	5-SELF-TEST.command

Double-click the fix icon, drag one or more video files into the window that opens, press Enter. Or from a terminal:

python cadence_fix.py "clip.mp4"          # diagnose and repair
python cadence_check.py "clip.mp4"        # diagnose only, writes nothing

Use the raw download. Not a file you have already run through an upscaler, and not one this tool has already repaired. The repair works by reading the original damage; an earlier pass has erased the evidence it needs. The tool checks for this and refuses rather than guessing.

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What it looks for

Five things can be wrong with a clip's cadence, they look identical to the eye, and they need different repairs. Doing the wrong one makes the clip worse — which is the whole reason this is one tool with one button rather than a folder of tools you choose between.

what it finds	what that is	what it does
PAD	every Nth frame is a copy of the one before it; the real frame was thrown away	repaints the wasted slot in place, ~1 frame in N
SEAM	a held frame, or a handful of frames simply missing	repaints the frozen slot — one frame each
PULLDOWN	a 25 or 30 fps render squeezed into 24 by dropping frames all the way through	rebuilds the damaged stretch at the real source rate
GRID	nothing repeated and nothing missing, but the steps alternate long-short on a strict beat	moves every frame back onto an even grid
CLEAN STATIC IRREGULAR	nothing wrong: even motion, a deliberate freeze, or genuine fast motion	nothing at all

It tells you which, and what the evidence was, before it touches anything — and 2-DIAGNOSE-ONLY shows you the same reasoning without writing a file.

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What it will not do

This is the part most tools leave out, and it is the part that makes the rest trustworthy.

• It will not change the length of your clip. Not by one frame. If the only possible repair would make the clip longer, it refuses and tells you why.
• It will not overwrite anything. A second repair of the same clip becomes _even_2, never a replacement, so you can always compare.
• It will not guess between two explanations. When nothing in the clip favours one reading over another, it says so and stops.
• It marks its own failures. Every repair is measured and re-diagnosed afterwards. If the invented frames came out as double images, or the clip is no more even than it was, the file is written as _even_REJECTED and the tool exits with an error. Keep your original.
• It will not work on a file that has already been processed. See above.

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A whole timeline at once (DaVinci Resolve Studio)

resolve/ holds a companion script that reads the clips on a video track of the timeline you have open, repairs the ones that need it, and stacks each repair on the track directly above its original — so you toggle the top track on and off to compare. Nothing on the source track is touched.

Windows   resolve\EVEN-FRAMES-IN-RESOLVE.bat
macOS     resolve/EVEN-FRAMES-IN-RESOLVE.command

Requires Resolve Studio — the free version has no scripting API — and Preferences → System → General → External scripting using: Local. It is slow, minutes per clip, and it runs outside Resolve on purpose so you get a progress report instead of a frozen application. resolve/README.md has the details.

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Where the repaired frames come from

Where a frame has to be invented, it is painted from the two real frames either side — by optical flow or by averaging, whichever measures less damaging on that particular clip. Both are tried, on that clip, and the choice is printed with the numbers behind it.

An invented frame is then checked three ways: for double images (two pictures superimposed — the characteristic failure of averaging over fast motion), for fine detail against the frames beside it, and for whether the motion actually came out even. If your clip moves faster than optical flow can follow, it says so rather than handing you mush with an encouraging word on it.

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Files

cadence_core.py        the engine: measures, classifies, plans. All the thinking.
cadence_fix.py         diagnose, then apply the one repair the clip earned
cadence_check.py       diagnose only
cadence_selftest.py    break a known-clean clip six ways, check the repairs
run_tool.py            the launcher the icons call
timing_check.py        does a repaired clip still line up with its original
resolve/               repair a whole timeline track (Resolve Studio only)
cadence-log.tsv        written as you go: one row per clip per run
docs/                  how it works, and the history of how it got here

cadence-log.tsv is worth knowing about. Every run appends a row with the verdict, the scores behind it, the frame counts, and the before/after measurements. When a clip comes out wrong, the numbers that produced the wrong answer are already on disk.

Needs only Python 3 and ffmpeg. No numpy, no pip install, nothing to build.

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Licence

MIT. Do what you like with it.

Credits

Built for the Moon Phase Chronicles AI-film project, where the stutter was costing more time than the shots were. Released free with the hope to raise the floor of AI films quality.