DVR versus NVR IP video

The huge advantage of architecture based on NVRs is that they can be located anywhere on a network – at the monitoring center, adjacent to camera clusters, on the edge of a network, collected together in a hardened environment, indeed anywhere at all. In use their location is transparent to an operator – he or she simply calls up the recorded video stream to be viewed and, provided that they have the necessary authorization there it is. NVRs record and replay simultaneously, and recordings on any one machine can be remotely viewed by a number of authorized operators spread across the network simultaneously, all totally independently and without affecting each other.

The importance of the independence of physical location, well away from the cameras if necessary, should not be underestimated – IT Managers are notoriously zealous in safeguarding their network capacity and rightly so, but by calculating the data flow requirement across the network and strategically placing NVRs accordingly, the impact of video streaming on bandwidth usage can be minimized. Typically an NVR might be placed on a Local Area Network (LAN) and near (in network terms, not necessarily physically) a camera cluster so that the load is carried by the local LAN capable of absorbing it easily, thus saving capacity on other, perhaps more restricted, parts of the network. The IT Manager can specify what level of bandwidth he is prepared to make available for video streaming and this can be set as a cap, so that it is not exceeded under worst-case conditions when in operation.

Then, when a recording is required at any other point on the network (typically “at center”, but not necessarily so) it can be called up seamlessly by the operator, streamed down and then analyzed, viewed (not the same thing) and acted upon accordingly.

To assist in the calculation of data flow requirement and disk storage capacity requirement spreadsheetbased calculators are available enabling these numbers to be calculated on a camera-by-camera basis using such parameters as the scene type (busy street / internal corridor etc.), functionality of the camera (PTZ under continuous operator control / static for ID purposes etc.), picture resolution and update rate in frames-per-second requirement, and if motion-sensing is used the motion frequency and type.First came the camera and monitor, closely followed by the Video Cassette Recorder (VCR), recording one video stream to a 3-hour tape at 25 frames per second and often triggered by an input device (raid button in a bank, for example). Technology then brought us the multiplexer, which allowed several streams of video to be recorded onto the same tape and separated out into discrete, viewable streams on replay and the time-lapse VCR which enabled the dropping of frames and in so doing permitted a 3-hour tape to be used over much longer periods, albeit at the cost of lost information.

The 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 DVR’s 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.


Many limitations still apply, however, not the least of which being that if it fails you’ll have most probably lost all your recordings (or they may not even have been made in the first place). This is not true of NVRs which can be used in “mirror” mode – see below. On the subject of reliability if you are going to use a DVR make sure that the one you’re proposing incorporates an industrial grade hard disk drive (HDD) and not a domestic one, or failure might be a lot sooner than you think (most DVR failures arise from overworked and overheated hard drives) - ask the manufacturer which drives he uses.

Like most other things in this world the actual performance obtained from a DVR, its ease of use and reliability will depend upon the manufacturer, individual model selected and price paid.

And so to the NVR
The Network Video Recorder heralds the arrival of the next natural point in the development of recording technology.

It is important to differentiate between DVRs and NVRs, as both are often termed ‘digital’. A DVR digitally compresses analog video feeds and stores them on a hard-drive, the term ‘digital’ referring to the compression and storage technology, not the transmitted video images. The DVR therefore has to be located near the analog feeds. In contrast an NVR stores digital images directly from the IPnetwork.

Therefore the most obvious difference between the DVR and NVR is that whereas the DVR records from analog streams provided from analog cameras the NVR records video streams that have already been encoded at the cameras. Thus you find no video connectors anywhere on a NVR; it’s input and output is IP data comprising compressed and encoded video. This will typically be in MPEG-4 format which has enjoyed widespread adoption in the CCTV industry as the current compression technology of choice, due largely to its efficiency.


NVR in a box!


The typical NVR solution simply requires a PC platform and hard disk storage. However, for more demanding fault tolerant applications NVRs can be packaged in stand-alone units. For example IndigoVision’s range of NVRs includes ‘NVR1.5’ which is a selfcontained rack mounted, Linux based, unit that has a removable hard disk drive. Any number of disks can be swapped out providing increased storage capacity. Typically a single disk will store 4 months of continuous full frame-rate high quality digital video. In addition disks can be moved between any NVR1.5 on the network allowing for example, remote recording with archiving and playback at a central location. It has built-in redundant power supplies and network connections and recordings can be mirrored to multiple NVRs around the network