synchronizing two devices, there are two usual methods:
frame lock sync and trigger sync.
Continuous frame lock sync has the slave constantly checking and adjusting its relationship with the master device.
In trigger sync the slave only synchronizes at the start - relying on both devices keeping accurate speed to insure synchronization.
Computers have a difficult time making constant speed adjustments so most lower-end systems have only trigger sync. For short sequences it generally poses no problems. Where one might have trouble is when the masterís speed is less than reliable, as often is the case with home entertainment vhs decks.