D-Link DCS‑6010L User Manual page 50

Section 4: Configuration
Size of each file for recording:
If this is selected, files will be separated based on the file
size you specify.
Time of each file for recording:
If this is selected, files will be separated based on the
maximum length you specify.
File Name Prefix:
The prefix name will be added on the file name of the
recording file(s).
D-Link DCS-6010L User Manual 50