Currently, Sync Out TTLs start as soon as the workflow is started in Bonsai, because the miniscope sensor works as a free-running camera, as opposed to being tightly controlled in hardware like in an industrial behavioral camera.

In the Miniscope-DAQ-qt software, sync out TTLs are supressed when acquiring (streaming data) but not recording to file (like the typical triggered usage of an industrial camera).

Users expect Sync Out TTL toggles to correspond 1:1 with frames recorded to file (barring data loss), like this schematic (top) as opposed to what happens now (bottom).

As far as I understand, at the moment the only way to recover only the TTLs of recorded frames in the Bonsai library would be to record both the sync out and the trigger in signal (if triggering the recording via hardware - and if using a virtual trigger line I'm not sure if software timestamping would be reliable).