The DVR is the most vital aspect in any surveillance camera system. Many of the most advanced features of a security camera could be limited or incompatible if the DVR does not support it. In the CCTV industry, you always get the quality that you pay for.
These 3 factors have to be considered when shopping or asking a tech:
#1: Live Display Resolution
The live resolution output of your DVR is directly proportional with the sharpness and clarity of the camera. Take the resolution 960H, for example. 960H is the name of the resolution resulting from (960 x 582), which are dimensions for pixel lines. There are 960 vertical pixel lines by 582 horizontal pixel lines, which equals 558,720 total pixels (or approx. 0.5 Mega Pixel).
Demonstrated by the photo above, 960H is in the middle for image size. If we were to stretch out that image to that of 1080p HD (2,000,000 pixels or 2 Mega Pixel), it would become more and more unclear. That is because that "stretching" is literally stretching the pixels to produce a larger image: resulting in a blurred picture. Basically, the more pixels you have available on your monitor + DVR ability, the clearer the image.
#2 Recording / Playback Resolution
Yes, there is a difference! We've had plenty of customers ask us why they can get a DVR online for so cheap. This is why: some brands advertise that they produce HD 1080p live display, and they do to a point. Watching the cameras live may be at this resolution, but the DVR records the footage in a lower quality.
This is critical, because when you go to download footage and submit it as evidence, it takes a serious drop in clarity and frames per second (making a fast moving object a blur). Take a look at the example below:
#3 Video Compression / Coding
Alright - time to get a bit more technical. This factor explains the science behind the difference in recording and live display resolutions.
Video compression is related to the processing power of the DVR. Just like how a computer with an obsolete processor makes even pulling up the calculator a slow task, the compression ability of your surveillance system is dependent on its ability to process the data it is recording. As displayed in the example above: recording at the resolution 960H captures 12 frames per second. However, when recording at a lower resolution, it is able to process 20 frames per second. Dropping the quality of resolution allows for this rise in speed.
Say you have an 8 channel DVR that records at 1080p. When you plug in only 4 cameras, it is able to process and record all 4 at that resolution. However, if you were to load it up with all 8 cameras, the DVR has to spread its processing power over more cameras - thus dropping the resolution and frame rate of them all.
When we talk about NVRs (Network Video Recorders), this data comes in the form of bitrates. Each camera has a range of bitrates (data transfer) - from a minimum to a maximum depending on the quality and speed of the imaging. A good quality NVR will compress the video in H.265, also known as High Efficiency Video Coding. In this case, the footage is more easily processed and even comes in smaller packets that take up less space on the hard drive and allow you to record more data with less memory than H.264 compression. This factor will be further explained in future blog posts.