My camera sometimes records only really briefly even when there's ongoing activity. Last night someone came into my drive and started trying the doors on our cars. The camera didn't start recording until he'd been there a while, as it showed him moving from the garage end of the drive back towards the exit, so presumably the security lights would have already been on for several seconds by the time the camera started recording. It then only recorded for just one second, despite the fact the man was still there, still lit up by the security lights, and still moving.

Luckily he didn't get into our cars, although he did get into a neighbour's car parked a few houses away. Our footage is useless, though, because it started too late and stopped too early. 

Why would it do this?