In this article you will understand what a DVR is and what are the key factors you should evaluate when looking at a catalog of a product.
When you finish reading this article you will also have a better understanding of what are the transmission and recording technologies used by a DVR.
Technical definition of a DVR
DVR stands for Digital Video Recorder. It's a device that converts the analog signals from a CCTV camera to digital format, store the information into a hard drive and also send live video stream to other devices on the network.
A DVR is not 100% analog
A CCTV system that has a DVR is not totally analog. The cameras send video signal in analog format and the DVR converts these signals to the digital format before recording and sending over the network.
So when you're working on a CCTV project that has at least one DVR, your project is not analog, it's actually a hybrid CCTV project.
The different technologies of DVRs
Now you know that DVRs have hybrid technology (analog / digital), and that most of the security cameras that are connected to DVR input have analog technology. Let us take a better look at this subject.
There are several different DVR options on the market and this can generate some confusion at the time of making your decision on which one is better.
You may have noticed that some DVR dealers offer different types of DVRs always stating that they have the best option bu using acronyms like HD-TVI, HD-CVI and AHD for example.
These acronyms represent the transmission technologies used by the analog cameras that those recorders can work with.
In this article, however, apart from the above mentioned technologies, I will explain what are the differences between different DVRs related to the recording and playback capacity.
DVR recording resolution
The quality of recording and viewing depends on several factors and one of them is the resolution, which is very important to see details.
When you are shopping for cameras and recorders, one of the things you should be aware of is the resolution that you should use in your project.
CIF, 2CIF and 4CIF Resolution DVR
Common Interchange Format (CIF) is a format that was created in 1988 for video teleconferencing systems and has been adopted in CCTV systems.
It's a digital resolution. If you have a camera or recorder that can work with CIF resolution, this means that the image generated has 352 x 240 pixels.
Below is an example of a catalog that shows a 16 channel DVR with CIF.
At 2CIF resolution the amount of pixels in the horizontal is doubled, so they are 720 x 240 pixels, which makes the image long so it is not so popular.
The 4CIF resolution doubles the amount of pixels both horizontally and vertically for a total of 720 x 480 pixels, which makes the image bigger and more interesting for recording, so it is more commonly used in CCTV.
720p and 1080p resolution DVR
These resolutions are very common now in cameras and DVRs that have the HD-TVI, HD-CVI and AHD technology mentioned above.
720p originates from the amount of pixels in the image that is 1280 x 720 horizontally and vertically respectively. If you multiply these pixels you will get a total of 921,600 pixels, that is equivalent to 0.9 Megapixel,
1080p originates from the amount of pixels in the image that is 1920 x 1080 horizontally and vertically respectively. If you multiply these pixels you will obtain a total of 2,073,600 pixels that is equal to 2 Megapixel,
See an example of a DVR with 1080p resolution:
These resolutions are not unique to a single brand, in the market it is very common to find different DVR brands with these resolutions.
MegaPixel resolution DVR
So you can say that the resolution of your DVR is 1080p or 2MP, But there are still higher DVR resolution on markets that goes beyond the 2MP.
Manufacturers such as Dahua and Hikvision have 3MP, 5MP and 8MP DVRs.
These devices were quickly spread around the world through these manufacturers and through other brands that use their technologies.
So it's common to find catalogs with camera and recorders with resolutions up to 4K. But obviously the price will be much higher.
DVR Frame rate
Another important factor for a DVR is the amount of frames per second it can record. This information is found in the catalogs as FPS (Frames Per Second).
See an example of a 30 FPS DVR (per channel)
The higher the number of frames, the lower the robotization effect of the image, which means you can see a smoother, smoother image.
The DVR will use an algorithm to convert to the digital format and compress the image to save storage and bandwidth over the network. This process is done by CODECs
Most modern DVRs use more advanced CODECs like H.264+ or newer H.265 and H, 265+ to compress video without losing quality.
To learn more about CODECs read the following article:
It's necessary to learn more about DVRs before go shopping. Obviously there are numerous other functions and details to take in consideration such as brand, dealer warranty and technical support.
Anyway, now you have enough information to make a better choice
Want to learn more ?
If you want to become a professional CCTV installer or designer, take a look at the material available in the blog. Just click the links below:
Please share this information with your friends...
Claudemir Martins is a former Samsung Engineer with 18+ experience in the surveillance industry. He has been traveling around 17 different countries to teach people how to design, and install CCTV systems.