Why AI video motion looks choppy, and what helps

The symptom: correct frame rate, uneven motion

The file says 24 frames per second, every frame is different, nothing is dropped. And yet a moving car, a walking figure or a pan briefly lurches forward. It looks like a stumble in the motion rather than a general lack of smoothness.

What we measured in Seedance 2.0 clips

We built Frame Repair after measuring the motion in our own Seedance 2.0 clips. About 600 tracked points per frame, checked forward and backward, give the size of each motion step. In smooth motion those steps are roughly even. At a hitch, the step suddenly doubles.

In most of our test clips that happened roughly once a second, in others only a few times per shot, and one clip had a jump on every fourth frame. We have not tested other models systematically, so we do not claim the pattern looks the same everywhere.

We describe what we measured, not why a model produces it. The cause inside the model is not something we can verify from the outside.

Four things that all get called “choppy”

1. A motion jump

One step in the movement is about twice as long as the steps around it. Every frame is different. It happens at specific moments, the same in every player. Fix: rebuild the missing in-between frame at that spot.

2. Duplicate or frozen frames

Two consecutive frames are identical, so the motion stops for a frame and then carries on. Stepping through, you see no change from one frame to the next. Fix: remove the duplicate, or replace it with a computed frame.

3. Frame rate conversion

Converting 24 fps to 25 or 30 fps by repeating or blending frames creates a regular pattern of uneven steps or soft, double-exposed frames. It only appears after the conversion and repeats at a fixed interval. Fix: stay at the clip's native rate, or use motion-compensated conversion.

4. Playback judder

A 60 Hz screen cannot give every frame of a 24 fps clip the same screen time, so slow pans judder evenly across the whole clip. It changes with the player and the screen, not with the file. Fix: nothing to repair in the file. Check on another screen or in your editor.

Checklist: which one is it?

1. Does it happen at the same moment in every player and on every screen? If not, it is playback.
2. Did it only appear after you changed the frame rate? Then look at the conversion first.
3. Step through frame by frame at that moment. Two identical frames in a row: a duplicate frame.
4. All frames different, but one step about twice as long as its neighbours: a motion jump.

Fixing a motion jump

The fix is to put the missing in-between position back: compute one new frame between the two frames that are too far apart. You can do that by hand in an editor with optical-flow retiming, or let Frame Repair find every jump and rebuild them in one click. The step-by-step version is in How to fix stuttering AI video.

Why not interpolate the whole clip to a higher frame rate? Frame interpolation for AI clips explains why that leaves the jump in place.