Judder is visible jerky motion in video — usually most noticeable on slow camera pans across a static scene like a wide shot of a landscape or a slow sweep of a stadium. Instead of moving smoothly across the screen, the picture appears to step in tiny, distracting jumps. The cause is almost always a frame-rate mismatch between what was shot and what the display is showing.
The classic example: a 24 fps film played on a 60 Hz TV. The display has to show each film frame for some number of TV refreshes, but 24 doesn't divide evenly into 60. So the system uses the old telecine 3:2 pulldown trick — showing one film frame for 3 TV fields, the next for 2, and repeating. On a fast cut it's fine; on a slow pan, the uneven cadence becomes visible as judder. Many modern premium TVs offer a "true cinema" or "true 24p" mode that runs the panel at a multiple of 24 (48, 72, 120 Hz) precisely to eliminate this.
For a streaming product, judder is mostly a downstream playback issue you can mitigate but not entirely fix. Authoring at the native frame rate of the content (true 24 fps, not 29.97 with pulldown) and delivering at native frame rate rather than converting to a "TV-friendly" rate gives the most reliable result — modern smart TVs and players handle the timing better than they used to. Motion interpolation features ("Motion Plus", "Motion Flow") on TVs try to smooth judder by generating intermediate frames, but they introduce the "soap opera effect" that destroys cinematic feel. The pragmatic rule: ship 24p as 24p, ship 60p as 60p, don't try to convert.
