A digital video recorder stores video from analog cameras, usually brought in over coax, and serves it for live viewing and playback. It digitizes and compresses the incoming signal. Hybrid recorders add a few network camera channels, which is how many sites bridge from analog to IP.
The recorder is the part of the system that holds the evidence. In an analog installation it also converts the signal into something a modern client can use.
DVR and NVR
A DVR takes video in as an analog signal and encodes it. An NVR receives streams that are already digital from network cameras. The practical difference is the cabling and the distance: coax to each camera, or a network link to a switch. Hybrid recorders accept both.
Extending a DVR installation
Check the recorder’s supported formats and channel count before adding cameras, and confirm the disk has room for the added bitrate. A DVR at its storage limit shortens retention rather than refusing the camera, which is easy to miss. Test playback and export after any change.