On December 12, 2016 at 01:39, Ernie Gilman said...
I've always wondered where those cameras get the temporal shift mechanisms that allow them to record before they sense movement. I suppose they're supplied by Douglas Adams.
Buffer (as in RAM). The buffer is constantly being filled with the current video, overwriting the oldest with the newest. When an event happens, the video from the buffer (with whatever parameters have been set), dumps to the storage device = hard drive, SD card, etc...
