HD-CVI DVRs, High Definition Composite Video Interface, in a summary.. With HD-CVI DVRs you now are able run a high definition 720P over coax, not only that you can do that but also to a distances of up to 1500ft without any issues, you can now utilize your existing pre-ran RG59 or RG6 Coax cable and upgrade your current standard low resolution analog cameras to High definition 720P resolution, no need to change your cable, no need to change your power source or connectors, all you have to do is get the right number of channels HD-CVI DVR and HD-CVI cameras and your done and now you have a 720p HD security camera system for very low coast.