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Determining the Appropriate Camera
Increased security awareness and new technologies are the driving forces behind the expansion of the video surveillance industry. The market for global video surveillance is expected to grow to more than $9 billion by 2011. One of the key technologies behind this expansion is the megapixel IP camera.
Prior to looking at any type of recording option, you will need to define the goal of your video surveillance system. Applications are generally broken down into three categories.
General Surveillance: These are applications where the user is looking to view areas that don't require a lot of detail - such as traffic areas, general views of parking lots or simply wanting to detect that someone is in the area;
Forensic: These are applications where you need to view and recognize images - such as faces and license plates. Typically these requirements would be for both live and recorded images;
High Detail: Many of these types of applications are found in the retail industry. Typically these applications include the need to see both customer and employee faces as well as the details of the transaction.
Once you have determined the category, the next step would be to define your resolution requirements. Traditional analog cameras defined resolution by television lines (TVL). A typical camera would provide a total of 480 TVL. Recently, with the proliferation of digital/network video recorders, the market has evolved into defining resolution by the total number of pixels. A good rule of thumb for determining an application's pixel requirement is approximately 20 pixels per foot for general surveillance, 40 pixels per foot for forensic and 80 pixels per foot for high detail. After determining the pixel requirement, you will need to know the dimensions of the camera's field of view in order to make the appropriate selection. Typically analog cameras are recorded in images that contain 640 horizontal and 480 vertical pixels, where an image from megapixel IP cameras can be 1920 horizontal X 1200 vertical pixels.
Two last things to consider when choosing a camera are the storage and bandwidth requirements. These would normally be determined by the size of the image and number of images recorded. The more pixels that the image contains, the greater the file's size. As the file's size increases so does the amount of storage and bandwidth required.
There are other factors that should also be considered when selecting a camera - lighting, environment etc. By understanding the image the camera provides and the amount of pixels required to capture the image you need, you can achieve the optimum camera application.
Digital Video Recording: How NVRs Differ from DVRs
Now that DVRs have become commonplace, they are changing into different shapes and forms - such as network video recorders (NVRs) - to meet the varying needs of end users. Learn what distinguishes NVRs from DVRs, their strengths and weaknesses, and how they can be applied to various types of applications.
This article is intended to shed some light on NVRs, how they differ from DVRs, their benefits and drawbacks. It will hopefully give the reader some insight into where this technology is appropriate and where it is not.
An NVR is a system component that takes digital video streams and stores them on an array of hard drives. It also presents the images for later playback, archiving and manipulation. While this may seem like the function of all digital recording systems, there is a distinction between a NVR and a DVR.
All video systems can be divided into four distinct areas: image acquisition; analog to digital encoding; storage; and image retrieval. In fact, the key difference is the packaging of these systems.
A DVR packages everything but the imaging device (camera) in one box, with analog (BNC) inputs, software to view and retrieve the images, and hard drive storage generally in the same chassis. Sure, you can often add storage in the form of an additional hard drive (either internally or externally) and use additional software clients for remotely accessing the video, but it's essentially a one-box solution.
NVR-based systems retain the same functionality, but the NVR requires a digital stream that it can accept from one of two sources. If the system is using conventional analog cameras, they are fed to an encoder that converts the stream to an IP steam the NVR can record. These encoders vary in capacity. Some manufactures offer single-channel encoders that have one input (analog) and one output (Ethernet). Others combine multiple analog channels to provide an encoder with several inputs and a single Ethernet output.
The second source is a camera and encoder combined in a single unit. These are referred to as IP cameras, and the types can vary. Some units provide additional inputs to allow a single IP camera to encode signals from external analog cameras in addition to their own image. IP cameras are more expensive than analog cameras, larger because of their additional functionality and associated circuitry, and are not available in as many aesthetically pleasing configurations as conventional analog cameras. These differences are shrinking with the market acceptance of the IP camera and it is only a matter of time before increased industry volume and the associated economies of scale will erase the cost and size differential.
It is important to note that NVRs do not care where the signal originates - an encoder is an encoder, whether it is a standalone box or built into an IP camera. It is possible to mix and match IP cameras and legacy cameras (digitized through a stand-alone encoder) in to the same system, as long as the encoder or the IP camera is sending out an IP stream that the NVR can read. And that's a pretty big "if".
For the most part encoders and NVRs must be matched to ensure they will work together. While there are a few exceptions, most systems are still somewhat closed and compatibility is not a given. As this technology is more adopted in the future, standards will emerge and compatibility issues should ease, but we're not there yet.
Interestingly NVRs appear at both the top and bottom of the market. Enterprise systems by larger manufacturers are encoder/NVR-type systems that have become the standard for high-end applications and are generally considered the most critical and performance intensive. However, many smaller systems are built using IP cameras and software that is loaded onto a conventional PC that turns the PC into an NVR.
For the most part the mainstream market belongs to the DVR. With embedded and PC-based solutions available, these units are extremely cost effective and usually are easier to configure than NVRs. The variety of analog camera configurations available makes them compelling for many users. So why would you consider a separate encoder/NVR system?
There are several positives the NVR solution can offer. Because of their distributed nature, NVR-based systems allow a great deal of flexibility in configuration. In many larger applications, it means the recorder can be placed in a location that is more centralized and secure than can be easily achieved in a DVR-based system. NVRs also allow a level of storage pooling that is not available on DVRs. Since each NVR is capable of handling multiple video streams, the system can be configured to ensure that storage space is maximized. This allows the system to provide a predetermined time limit on video storage without wasting hard drive space.
NVR-based systems can also efficiently handle failures. If an NVR fails, many systems will reroute the IP data streams to a backup unit until the first is restored to operation. Coupled with the reliability inherent in RAID-based storage systems, available dual-redundant power supplies from many manufacturers, and controlled environments allowed by this distributed architecture of an NVR- based system, it is easy to see why this is the design choice for high-end enterprise digital video systems.
However, no system is perfect and there are some disadvantages to NVR-based systems. The first is bandwidth. Unless there is some level of data storage in the field device (which really makes the field device a DVR), the system is always consuming bandwidth. If the network link from encoder or IP camera to the NVR goes down, recording will stop. This almost necessitates a separate network for the digital video system and creates numerous opportunities for sabotage or other system failures.
One proposed solution is to distribute the NVRs, locating them closer to the field devices, but making the system look, smell and act like a conventional DVR system. This brings up the second disadvantage: cost.
Systems with NVRs are generally more expensive, unless they require one or more of the features that are listed as advantages. If centralized storage is required, it is frequently less costly to place encoders in the field than it is to run each camera back to the central point. If storage-intensive video recording is required, either because of resolution, frame rate or retention time, the pooled storage nature of the NVR systems may significantly decrease costs.
High reliability, the ability to record to multiple locations and other architecture-dependent features also swing the balance toward NVRs. But for many systems, the lower entry cost and modular nature of conventional DVRs is more appropriate. The complexity of NVR systems can also be a factor. With a DVR, you simply add additional DVRs when more inputs are required. NVRs require more complex calculations of the number of video streams that can be handled by a server, the amount of hard drive space available, frame rate, compression and other factors. These attributes often must be plugged into a spreadsheet to determine which part(s) of the system must be expanded if additional cameras are added.
One side effect of the proliferation of digital video systems is the sheer number of options available in the market. The increasing reliability and ease of installation for NVR-based systems allows them to be viable candidates for applications that may have been too complex to consider a few years ago.
With the speed and reliability of networks ever increasing, it makes sense to consider systems that utilize the network as an integral part of their design. This does not mean that the DVR is going to go away any time soon. It does mean that the DVR is transforming into a variety of different devices, one of which is the NVR.
