Author: Mike Norton
The Digital Video Recorder or CCTV NVR/DVR is an industry specific product central to any CCTV system. It arranges the camera footage on screen and it stores images from the cameras. In some cases the DVR has a third function whereby it allows you to remotely access your CCTV system via the internet or a local network. This DVR buyers guide explains what you should look at when comparing different recorders and explains what some of the key functions do.
A modern NVR/DVR will allowed you to view each camera in sequence or several cameras at a time via a split screen. The one issue with NVR/DVRs is that they can be quite complicated, learning the difference between all of the various features and technological advancements incorporated into today’s CCTV recorders can be a minefield. It doesn't help that the boffins who design and build NVR/DVR recorders are sometimes left too long in their darkened rooms and come up with wild and crazy features which massively over complicate their products and are rarely used.
Our HikVision recorders allow simple operation whilst at the same time, offer high levels of functionality to those who need it. We don't stock lots of different brands of CCTV products, there is no need! Our HikVision products will do everything you require of it. Concentrating on one range means we can offer unrivalled after sales support due to our intimate knowledge of the product.
Digital Video Recorders are the heart of the CCTV system and are used to record and control the CCTV cameras. NVR/DVR’s are available in different sizes depending on how many cameras are to be installed at the premises and the amount of archive footage that is required to be held by the customer.
The most common NVR/DVR we install to domestic premises are four camera units with the ability to store between 20 and 30 days of archive footage on an internal hard drive, although solutions of upto 64 cameras and beyond are available if required.
The DVR can display live and recorded images in many ways, the most common is via a or dedicated CCTV monitor, and we are also able to connect the DVR to the existing computer network at your premises, allowing all cameras to be viewed on any computer within that network. If that network has internet access then the images can be displayed on computers, tablet devices and smart phones anywhere in the world. See Remote live viewing for more of an explanation.
If an event occurs, footage of the event can be downloaded from the DVR to a computer or memory stick and a copy can then be passed to the Police for prosecution purposes.
MJPEG and H.264 - how the NVR/DVR squashes information into a smaller space
Left un-compressed the raw footage coming into the NVR/DVR from the cameras would soon fill up the CCTV hard drive. To get round the problem the CCTV boffins have devised methods of compressing the information down so it takes up less space. There are predominantly 2 formats in use - motion JPEG (or MJPEG) or H.264. Compression codec (compressor - decompressor) formats such as MJPEG & H.264 has uses far beyond the NVR/DVR in a CCTV system. Computers and the internet are a much larger market for the technology but the aim is the same. Squash information down so it takes up less space and can be sent across the internet quicker.
H.264 is the most efficient compression method and all our NVR/DVRs use this format. The big advantage H.264 has over MJPEG is that it compresses files down into a smaller size than MJPEG. Because the file sizes are smaller they take up less hard drive space resulting in more recording time for the same size hard drive.
DVR Recording speed - frames per second
A lot of people selling CCTV equipment place great importance on how many frames per second a DVR can record. Cinema projectors use 24 frames a second to provide perfect live motion playback. The human eye can generally detect around 10-12 frames a second. Unless you want to be the next Steven Spielberg, in which case you're buying the wrong equipment, then realistic movement is actually not that critical when it comes to CCTV, certainly not if it comes at the expense of image quality or the length of time you can store footage on your NVR/DVR.
We recommend a target of between 6 and 12 frames per second for CCTV use. This takes up a quarter/half of the space on your hard drive compared to 24 frames per second without costing much in footage quality.
Recording Modes - All our NVR/DVRs can be set to record in a number of ways
Continuous. This is our recommended recording method. The NVR/DVR records all the time, when the hard drive fills up it goes back to the start and records over the earliest footage on a rolling basis. Our NVR/DVRs allow you to decide what happens when the disc is full, you can opt to stop recording so it doesn`t just over write the earliest footage although we don`t recommend this.
Motion sensing. The DVR monitors the picture coming in from the camera. If it sees movement then it saves the footage from just before the movement and keeps recording for the next few seconds - you determine how long. You can choose which areas of the screen the DVR looks for movement in, you don't have to use the whole screen as a trigger area.
A word of warning about motion sensing - It is easy to get false alarms when using motion sensing, particularly when filming outside. Insect movement, spider`s webs blowing in front of the camera, changing light conditions and rain are all things that can trigger the motion event. To avoid this use small trigger windows rather than the whole screen. The best solution is to record continuously and use motion detection to generate bookmarks of potentially important information.
Alarm triggered. The DVR starts recording when triggered by an external sensor such as a PIR (passive infra-red) motion sensor or magnetic contact "reed switch". You can set how long the DVR records for after it`s been triggered. This method is reliable in terms of not generating false triggers but involves additional wiring and sensor hardware.
Scheduled. You can decide what type of recording takes place at various times throughout the day and on certain days of the week. This helps reduce the amount of space taken up on the hard drive but the downside is no recording takes place if an event occurs when the DVR is scheduled not to record.
How many days footage will my CCTV hard drive store?
There are a number of factors which will determine this, some of which we have already covered in this section. The main things to consider are:
Recording quality. The higher the quality the less time a given hard drive will record for. However we strongly recommend you use higher resolutions wherever possible. Choosing a lesser resolution compromises the effectiveness of your home CCTV system.
The number of frames per second you record at. This is something you can change without compromising your CCTV system. Rather than waste hard drive space recording at 24 frames per second adjust the DVR to record each camera at 6 or 12 frames per second. This will give a benefit in recording time for little or no material loss in performance.
The number of cameras you have on your system. Each camera requires space for its footage to be stored.
As a rough guide 1.5TB of hard drive space per camera will give around 30 days constant recording capacity on a system using H.264 compression and recording 24 hours a day at 12 frames per second at 1080P quality. Many retailers cheat and quote storage times based on lower quality resolution. This implies the NVR/DVR is better than it really is..
Always fit the largest hard drive your budget allows and be aware that doubling the size of the drive doesn't double its cost. Larger drives work out much better value per unit of memory. If there is any chance of adding additional cameras to your system once up and running try to account for the additional cameras in your choice of hard drive.
Why not save money and just use my computer for CCTV rather than buying a DVR?
A logical question, after all your computer uses a very similar hard drive. There are a number of reasons why we don`t recommend this.
Video data takes up a large amount of storage space. Multiples of 3 or 4TB HDD’s are becoming the norm in terms of what to fit in a NVR/DVR. All this video data filling up your computer could prove problematic. Your normal computer hard drive is not designed to run 24 hours a day and to be filled up to 100% capacity. Our hard drives are designed to handle this heavy usage.
You could find performance issues caused by the extra processing strain caused by asking your computer to handle the CCTV footage.
If your storing CCTV footage caused problems with your computer the results could spell disaster as most of us keep vital information on our PCs.
What gets stolen in a burglary? The PC - so not much use storing images of the break in there then! A DVR can be hidden away or kept under lock and key.
The software and capture card that fits in your computer costs money. It`s not hard to spend $1500 on a good quality PC, why not just spend the same amount (or less) on the right tool for the job - a NVR or DVR!