Monitor the hard disk on the recorder is what format without formatting
Some video recorders have several hard drives. A record after the automatic record in the next hard disk. After the hard disk, you can remove the archive, put on a new one. You can not remove, then a few hard disk cycle recording, and the earliest images erased.
Continuous monitoring, then, hard disk is full, automatically erased the oldest video, recorded the new. Loop video.
Commercialized, stereotyped surveillance video recorder format you do not have to consider. You only need to set the pixel (or fine level), several frames per second, date and time.
