Phi Nguyen - 2M CCTV
So, are you thinking about buying a security camera system? You got the cameras that you like. You know where you want to place them. You even hooked the cameras up to a monitor to see them. If you are reading this article, then you have probably realized, or were informed by someone, that you need something to actually recordthe footage from those lovely cameras.
The missing piece of equipment is a digital video recorder or DVR for short. A DVR recorder is a device that uses the digital video taken from security cameras and then stores that video onto a hard drive. We generally place DVRs into two classes, PC based and standalone.
If you decide that you require a PC based DVR over a standalone, the next step will be deciding on a DVR capture card or “video capture card”. This is the “heart” of the DVR, so to speak. This article is a guide to help you choose the right DVR capture card and one to fit your budget.
DVR Recording Frame Rate
When picking a DVR card, I like to first look at frame rates, particularly the recording frame rates. The industrial measurement for frame rate is frames per second or fps. Another commonly used term when talking about DVR cards is Real-Time Recording. Real-Time Recording is pretty much like the name implies, the rate at which you would see a scene as if you were there, seeing it with the naked eye. The rate for real-time recording is 30 fps per camera.
When looking for DVR capture cards, manufacturers will list a large number like 240 or 480 for frame rate on the spec sheet. That number is the total frame rate and is divided by the total number of cameras that the card supports. For example, a card with 60 fps made for 8 cameras would result in 60 / 8 = 7.5 fps per camera. Conversely, an 8 camera card with real-time recording will have a total frame rate of 240 fps, 8 Camera x 30 fps (real-time rate) = 240 fps.
Example Frame Rates for DVR Cards
So after looking at the different frame rates, you might have noticed that there is really not that much of a difference between real-time and say 20 fps or even 15 fps. So when picking a DVR capture card, you can save money by picking one that has less than real-time frame rate. Plus, almost all DVR capture cards allow for adjustable frame rates per camera, so you can choose to view the important cameras in real-time while the other cameras are set to a slower frame rate.
DVR Capture Resolution
After frame rate, the next important feature to look at when choosing a DVR capture card is resolution. The resolution is the number of pixels in an image, usually displayed by width and height. For security surveillance, the normal available resolutions are QCIF (176x120), CIF (352x240), 2CIF (704x240), and 4CIF (704x480). D1 (720x480) resolution is another resolution which is associated with DVR cards. Since 4CIF and D1 resolution are very similar, we will use 4CIF to describe the highest resolution for analog recording. Also, due to their sizes, QCIF and 2CIF resolution are not used much in the industry today, just something to keep in mind.
After we created the above graphic, we actually found a good video showing the Resolutions as well....
Contrary to the graphics above, 4CIF resolution does not produce a very large image size when compared to 1080p high definition resolution. Though 4CIF resolution does offer some advantages over higher resolutions. For one, a system with a resolution above 4CIF would require looking into IP technology which doesn’t use DVR cards and is much more expensive; we’re talking double or triple the price.
4CIF resolution also displays great image quality on most computer monitors, which are around 19 inches. DVR capture cards are designed for computer based surveillance systems, so you are more than likely going to view your cameras on a computer monitor. Another device that you might view your camera with is a mobile cell phone. I don’t know about you, but I don’t know anyone that carries around a cell phone with a 19 inch screen. For remote viewing through your mobile phone, CIF resolution is all you really need because of its small size.
DVR Card Video Compression
Another important feature to consider when choosing a DVR card is the video compression used for storing the images taken from the camera. I won't bore you with the explanation of video compression. Just know that the compressions available for you include MJPEG, MPEG4, and H.264. H.264 video compression is the only one you should concern yourself with as it is the best of the three. Plus right now, almost all the video capture cards use H.264 compression as the main compression method.
Remote Viewing Capability
One of the features that owners of a security system love to have is the ability to view their camera from a remote device such as a home computer or mobile phone. Manufacturers of DVR capture cards are well aware of this fact and make sure all capture cards have this capability. To view your camera, you simply need to use a web browser from whatever computer you are at or with an app for popular mobile phones such as the iPhone and Android phones. Of course, you need to setup up your surveillance system on a network to be able to remote view.
When selecting a DVR card, you should choose one that has an acceptable frame rate and resolution while also keeping your budget in mind. Remember that real-time is not as important at it is seems to be. Remote viewing and the latest compression technologies are available on all video capture cards, so no need to decide between them.
Creating a security system with a DVR capture card offers the user so many customizable options that all the possible features will not fit into this one article. So, be sure and check out the second part of our DVR capture card selection guide!