FLIR A6000 Series User Manual page 32

The pulldown menus show the following options: Sync Source can be Internal, External or Video.
Internal
External
Video
A6000 and A8500 Series User's Manual
Sync Sources
The frame sync is generated internally to run at the frequency
set by the user
The frame sync is generated externally through the Sync In
connect on the camera rear chassis.
The frame sync is generated from the internal video encoder,
locking the HD-SDI and FPA clocks together.
5 –Camera Controller
32