It is to do with codex.
In your case it is either a cheap Chinese DVR with no proper support.
Or your PC is missing important flash/video add-ons. (Not probable!)
I have seen this problem in the past and managed to find a solution for it, that is:
Do not use the cheap software provided by the CCTV manufacturers.
Connect to view your CCTV on internet explorer and that should work.
