DVR

The rapid development of video compression algorithms (JPEG, MJPEG, MPEG-4, etc.), computer processing speeds and a rapid reduction in data storage costs then gave rise to the DVR. This you could consider as being the functionality of a multiplexer together with a computer disk for storage in place of tape, all housed in the same box together with some additional ports for connectivity.

The DVR provides a convenient, if limited, replacement for the multiplexer + VCR combination and provides non-linear access to recorded material usually selected by camera ID, time and date. The consistency of quality of recorded material will in general be higher than that obtained with analog tape although the actual quality achieved may or may not be better, depending on the compression algorithm and individual configuration.
In general more programmable options for individual video stream recording parameters, (picture resolution, number of frames per second, trigger options, start/stop times etc), are available, but a DVR is only useful where the analog cameras are all cabled back to the DVRs location. Competent DVRs now feature UDP (CAT 5) network ports so that the device can be provided with an IP address and thereby become accessible over an Ethernet network.