Your projector runs at 50 Hz. Your software does not. That is the judder.

Two clocks that do not agree

Your machine renders frames at its own rate. The projector paints them at its own rate. When those two numbers do not divide cleanly into each other, some frames get shown twice and some get dropped — and because the mismatch is regular, the stutter is regular too. That steady, rhythmic hiccup is the fingerprint.

Why this bites harder in Europe

Broadcast and installed AV in Europe grew up around 50 Hz; computers and most content default to 60. Plenty of venue projectors, especially older installed ones, are still configured at 50 Hz — or they negotiate down to it over a long cable run without telling anybody.

So you arrive with a machine happily rendering at 60, plug into a display running at 50, and the mismatch is baked in before you have opened a single clip.

How to catch it before doors open

• Check the output, not the laptop. The rate that matters is the one the projector reports, not the one your screen is running at.
• Watch for the rhythm. Random stutter is usually load. Metronomic stutter is almost always refresh mismatch.
• Match, do not fight. If the projector is fixed at 50, set your output to 50. A clean 50 beats a fighting 60 every single time.
• Mind your clips. A 60 fps clip on a 50 Hz output will never be perfectly smooth. For installed 50 Hz rigs, 25 fps content is your friend.

The bit that costs you the show

None of this is hard to fix. It is hard to notice — at soundcheck, in a bright room, on a short clip, a 50/60 mismatch can look absolutely fine. It shows up two hours later, in the dark, on a slow moving shot, in front of a full room.

That is why LumaDeck Pro checks it as part of its pre-flight, along with media, VRAM, projectors and free disk: the point of a pre-flight is to find the boring problems while there is still time to fix them.