Digital video recorders or DVRs are still extremely popular video recording and storage devices. They have been around for over 20 years now. DVR started as a replacement for VCR and a multiplexer. It was a very innovative device back then where most of the video was stored on VHS tapes. A standard VHS tape could only store up to 4h of a full motion video. That was extended with a use of time lapse recording. Security VCR would record a frame every 3 seconds or even more. Video was choppy, it was very hard to retrieve and it required a lot of room to store all those tapes. Multiplexer offered the way to record a video from several cameras onto one VHS tape, but again, the quality simply wasn't there. And to find an event could easily take days for fast forwarding through the tapes.
Digital Video Recorders solved a lot of those issues. They were capable of recording a video from many cameras (up to 32) with a much better quality and a better frame rate. There was no need for changing and storing VHS tapes and the motion activated recording and search made it so much more efficient to record and store the video. The invention of the DVR made video surveillance system affordable for almost any business and many home owners. CCTV cameras were also getting better and more affordable. Video surveillance market was booming. We started to see security cameras popping up at the gas stations, retail stores and even residential homes. Over the years DVRs were becoming more and more advanced and more reliable. New features like remote access and live video broadcasting made it possible to keep an eye on your property from anywhere in the world utilizing the internet. The newest DVRs offer basically all the same features as NVRs and IP cameras. Video analytics, full remote access and management, on site and off site backup, user management, alarm and access control integration are just a few. Recording resolution have been improving over the years as well. Starting from 320x240 CIF resolution to currently up to 8MP 4K Ultra HD. The main difference between current DVRs and NVRs is that DVRs are used to process, record and store the video from every single camera connected. NVR basically just stores the video, while all the processing is done at the camera level. That is a huge bottle neck in the DVR based surveillance systems. Sending uncompressed full motion and high resolution video from the camera to the DVR requires a lot of bandwidth and that's why all the cameras are directly connected to the DVR usually via coaxial type cable. DVRs are also not capable of utilizing local area network for communication. All the wiring needs to be 100% dedicated for the video surveillance. Modern HD DVRs can record resolution up to 16MP, 8K and are a great option for any facility already pre-wired with coaxial cable or as an upgrade for older analog systems. Those are basically the only two reason why some customers still purchase DVR based video surveillance system.
As with NVRs, there are a couple of different DVR types:
- PC Based DVR, usually utilizing a pretty standard PC computer. Instead of purchasing a standalone unit, customer can purchase multi-channel video capture board and install it in the standard PC. There are a few advantages to those systems, they tend to be a little less expensive than standalone DVR and since the software is already running on the computer, it is easy to backup the video or pictures, as well as edit, or print them. Since the majority of the system is assembled in similar way to the PC, when a part goes bad, it is fairly easily to replace it. It is worth to mention that PC based DVRs were really popular in 2010' but currently the market is dominated by standalone units and PC based DVRs are a very rare find. Some of the biggest names famous for their PC based DVRs are GeoVision and Eyemax.
- Standalone DVR are by far the more popular choice. They are very affordable and mass produced in many different models and configurations by many manufacturers, out of which big three are Hikvision, Dahua and Uniview. This type od DVRs are all in one units, equipped with a hard drive(s) for video storage, power supply, video card and video capture board. They are usually Linux based and are very reliable. They come in many different configurations. Some major differences are: number of the video channels (cameras) supported, number of audio channels, storage capacity (number of hard drives), recording resolution and frame rate, video analytics capabilities and finally the technology supported. There are currently 6 major video transmission technologies. Analog and analog HD include HD-CVI, HD-TVI, A-HD and CVBS (standard analog). There are also 2 digital technologies: HD-SDI and EX-SDI. When purchasing a DVR we need to make sure that our cameras and the DVR use the same video transmission technology. The good thing is that most of the DVRs on the market are either 4-in-1 or 2-in-1 or even 6-in-1. 4-in-1 usually support A-HD, HD-CVI, HD-TVI and CVBS. 2-in-1 are usually reserved to EX-SDI and HD-SDI. And 6-in-1 supports all the formats. New DVRs often support IP cameras as well and can work as a hybrid units. It's a great options for some installations where older system and wiring is being utilized but some new camera locations are also needed.