Why Free-Running Cameras Drift Out of Sync

Every camera’s internal clock runs at a slightly different rate — a deviation measured in parts per million (ppm) from nominal. Left to run free (without a genlock cable or shared timecode feed), two cameras that start perfectly in sync will slowly drift apart as their clocks diverge. For most multi-cam shoots this drift is invisible for a while, but it eventually accumulates into a visible frame offset that breaks sync in the edit.

Jam Sync vs. Genlock

Genlock physically locks cameras to a shared reference signal continuously, so drift never accumulates — but it requires cabling and hardware support most cameras don’t have. Jam sync is the practical alternative: periodically feed each camera the same timecode value, then let them free-run in between. This calculator tells you how long you can let cameras free-run before drift exceeds your tolerance, so you know how often to jam-sync.

Where the PPM Numbers Come From

Camera manufacturers rarely publish exact clock accuracy, but professional cinema cameras with temperature-compensated crystal oscillators typically hold within 0.2–1 ppm, while consumer and prosumer cameras can drift several ppm or more. If you don’t know your camera’s spec, choosing a conservative (higher) ppm value and jam-syncing more often is the safer approach.

This tool is especially useful for:

• Multi-camera shoots without genlock cabling, needing a jam-sync schedule.
• Documentary and event crews running several cameras over long takes.
• Editors troubleshooting why long multi-cam clips slip out of sync near the end.