Video Recorders

Introduction

The purpose of a Video Surveillance Camera is to enhance the safety and security of a facility and it employees. With this purpose in mind you need to decide who, what, when, and where that the Video Surveillance Camera will view and record. Next you must determine how long you would like to keep this information. Do you need real time search of archived information? Will the system be constantly viewed or just reviewed when needed? What levels of detail do you need, a face or a large general overview, or both? Here we want to explain more about the different kinds of recorders in video surveillance.

Video Recorders

The Video Recorders came with the camera and monitor first, closely followed by the Video Cassette Recorder (VCR), technology then brought us the multiplexer, which allowed several streams of video to be recorded onto the same tape and separated out into discrete and viewable streams. Nowadays there are different types of Video Recorders such as DVR and NVR. One of the problems the user must face when choosing a security system is whether or not they want to record with the NVR or DVR. For more information here is a brief description of the most important types of Video Recorders such as DVR and NVR.

Digital Video Recorders

DVR is defined as Digital Video Recorder, a security device that records video in real time from analog cameras to one or more hard drives. In fact, it is a VCR which uses a hard drive to record video instead of video tapes. Unlike VCR, DVR can also pause live TV by recording the current show in real time. The videos from IP cameras can be recorded on DVRs but a codec is needed for each camera to convert the IP video stream back to an analog signal so it can be recorded. Some DVRs connect to the network and can be viewed using the camera.

A DVR typically has its own motherboard, processor, analog-to-digital converter, and one or more disk drives. Configured DVR for physical security application receives analog video signals from closed-circuit television cameras, and then converts them to digital signals to record and view. Any good DVR system provides advanced functions over VCR technology including video searches by event, time, date and camera.

DVRs have the following internal components:

1-   An analog to digital converter, or encoder, which converts the analog video signals into the digital domain.

2-   Digital storage, usually hard disks, where digital representation of the analog signals is stored and is ready for use.

3-   A database, relating the digital information to references; time, alarms and other metadata, enabling the video information to be retrieved and displayed quickly and easily.

4-   Digital to analog conversion and replay controls. These are usually found more in smaller, standalone DVRs and less common in enterprise level DVRs.

5-   An operating system, which runs the whole DVR.

6-   A computer network interface, found in more recent DVRs, to allow the DVR to be interrogated remotely.

DVRs have an input for every camera connected i.e., there is a direct connection, typically by BNC, UTP or fiber between each camera and the DVR. For example a 16 channel DVR will have 16 physical connections, one for each of the cameras.

Network Video Recorder

With growing popularity of computer network and video compression technologies, next generation video surveillance systems are moving to digital and IP networking. NVR is defined as Network Video Recorder, a device for recording digitized IP video streams, originating either from analog cameras connected via IP encoders and/or IP cameras where the IP video streams are created inside each camera. It is a device with a built in software program called Video Management Software (VMS) that provides recording of surveillance video in a digital format to storage devices such as memory card, disk drive, USB flash drive, etc. NVR includes a computer and special software required to not only record the video but also allow many people to view real time and recorded video that includes both the computer and special video management software. The computer can use Windows, UNIX or MAC operating system.

An NVR does not have any video capturing hardware, so it is used in conjunction with network cameras that capture images and transmit compressed video over the network. NVRs can be written and read simultaneously, meaning that viewing and analyzing one stream of video is possible at the time another stream is being written. Since NVR is commonly equipped with hot-swappable additional storage, its content can be recovered easily. There are different types of NVR security system such as 4, 8, 16 and 32 channel NVR systems with different number of bays for supporting multiple hard disks and scalable storage.

Network video server is a computer that runs special VMS (Video Management Software) that is used to record video from IP cameras and is so similar to NVR in that they both record the video. The NVR comes with VMS already installed while the video server does not include the VMS software. The video server runs windows operating system and is more flexible than NVR because it is easier to expand but NVR has a fixed limit to the number of cameras it will support.

NVRs have the following internal components:

1-   Digital storage, usually hard disks, where the digital IP video signals are stored and are ready for use.

2-   A database, relating the digital information to references; time, alarms and other metadata, so that the video information required can be retrieved and displayed quickly and easily.

3-   Digital to analog conversion and replay controls. These are usually found more in smaller, standalone NVRs and less common within enterprise level NVRs.

4-   An operating system, which runs the whole NVR.

5-   A computer network interface, which is the primary input for IP video streams into the NVR and also the primary way of connecting playback equipment in large systems.

RLN8024U-MF and RLN1632U-MF are two models of Red Leaf NVR.  

Main differences between DVRs and NVRs

While digital video recorders (DVR) are a very good choice for home surveillance, they are not your only option. A network video recorder serves the same intended purpose of recording activity in and around your home, but does so by employing a different process. Here we notice the main differences between NVRs and DVRs, such as their structures, costs, reliabilities, flexibilities, etc.

NVR is a single common input, a network connection for all the IP video inputs. This common connection is also used for the connection of playback client PCs. A network switch connects individual IP cameras, IP encoders and playback PCs to this common single connection. DVR device just records the transmitted videos from analog cameras to play them in certain time. To implement, analog cameras must connect to DVR device separately via a coaxial cables which leads to a complex cabling scheme with a high cost, in contrast to the NVR which only one network cable is attached to the system that contains the video signal from multiple cameras.

NVR records images under a network, while DVR performs recording images just as a memory card. In fact, the big difference between DVR and NVR is that a DVR digitally compresses analog video and stores them on a hard drive, but NVR stores pre-compressed digital image by IP cameras. In other words, With a NVR, the video input comes from the network, so coding images in IP cameras leads to higher data transfer rate in spite of high volume information compared to the transfer rate of coaxial cables related to DVR system. Also, by the compressing images in IP cameras, the high quality images of these cameras will not be degraded during transmission. This difference makes the NVR an efficient recorder.

NVRs are less expensive than DVRs. The internal components inside an NVR are less than DVRs. The A/D encoding takes place outside of an NVR in the IP camera and IP encoders. The minimum that one need in an NVR is single network connection, operating system, database and storage devices. The OS and database can be software so only a minimum amount of hardware is needed and also A/D conversion circuit needed in DVR is completely eliminated, saving cost. NVRs are more reliable than DVRs. The more components, the more there is to go wrong and the less will be the reliability of the device. NVRs can produce more details than DVRs. DVRs record analog video signals and the maximum resolution capable of being recorded is that produced by the analog cameras themselves. NVR can record IP video streams and also can record megapixel cameras, but DVRs can't. NVRs can deliver much more high definition recordings than DVRs, allowing fine detail to be discerned from a surveillance view even when the image is zoomed in digitally. The DVR takes an analog signal and processes and compresses it and stores it. The NVR takes the stream directly from IP camera and archives it, because the cameras are already putting out a JPEG or MPEG, so there is no need to perform a compression at NVR side. NVRs are more flexible in their application than DVRs. NVRs can record analog camera and IP camera of both standard and megapixel resolution. DVRs can only record analog cameras. DVRs have BNC connectors for analog cameras but NVRs use Ethernet cable.

Due to high quality images in IP-based camera, the video recorder should be able to support the high volume and quality without destroying the transmitted video information. It is worth mentioning that DVRs can't connect to IP cameras directly, thus a digital to analog converter is needed. However, the quality of images is degraded severely, so it is not recommended.

On the other hand, to view the video that was recorded, being at the DVR place is needed, but with an NVR, due to it being on a network, it can be viewed remotely. So the accessibility is the other difference between NVR and DVR.

The main differences between NVR and DVR are summarized in the following table.

 

 

 

Source : articlesbase.com