David, great input, thank you! The suggested SuperPassword was tried, worked as promised generating however the alpha-numeric patterns only, while my password seems to be strictly numeric suggesting the front panel keypad use according to its input screen, see picture.
The DVR recognizes USB mouse attached but not USB keyboard.
My guess about the brand: this is Edac Security Inc, US--Nigeria company. Their website lists a phone, a fax, and an email, neither answers though...
Any additional thoughts are welcome, running out of ideas. Thanks!