Encoder Tutorial

By: Ethan Ace, Published on Apr 26, 2012

As more users look to upgrade aging analog camera systems, encoders play an increasingly vital role. Though not as frequently discussed as IP cameras, knowing how to properly apply encoders is key for use in these upgrades, as well as specialized applications. In this tutorial, we cover these topics, including:

  • Applications for encoders
  • Encoder form factors
  • Standard and optional features of encoders

For more information, users may also see our integrator survey results, detailing integrators' favorite encoders, with commentary on each of the favorites.

When to Use Encoders

While most VMS installations use IP cameras in new locations, there are two main applications in which encoders are commonly used:

Analog Conversions

Encoders are most commonly used when taking over existing analog cameras. This potentially reduces cost compared to new IP cameras, as less cabling and installation labor is required, since work is performed mainly at the head end, with an encoder installed in place of the existing DVR or DVRs. Due to falling prices of megapixel cameras, however, maintaining existing, in many cases aged, analog cameras approaches the price of installing a new low-cost megapixel camera. For this reason many users prefer to forego encoders and install new cameras, instead.

Specialized Cameras Applications

The second common use for encoders is to connect specialized cameras to the surveillance system. There are a few common examples of this, by no means a comprehensive list:

  • Thermal cameras: Only in the past 1-2 years have IP thermal options become available, with many new models still requiring encoders. This is especially true of many pan/tilt and dual-imager thermal models.
  • License plate capture cameras: Few IP license plate capture cameras are available, making analog cameras with encoders the de facto standard. Users should beware, however, as interlacing issues may be a problem in some cases, and not all encoders support de-interlacing. We covered this topic in a past LinkedIn discussion.
  • Door intercom stations: As we discussed in our door intercom tutorial, most door stations with cameras provide analog output only. Encoders may be used to integrate video, and optionally I/O with the VMS system.

Encoders vs. Hybrid DVRs

Where the VMS system supports hybrid recorders, they may be an option instead of encoders. Using a hybrid DVR allows cameras to be directly connected to the recorder, instead of requiring a separate encoder, and network configuration. However, our comparison of the two shows that encoders are typically most cost-effective.

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Standalone Encoders

In many cases, standalone, fixed channel count encoders are preferred. These are available in several types, to fit a variety of applications:

  • Compact: Where space is a concern, compact encoders may be used. These units, typically single channel, may fit directly in camera housings or small enclosures, reducing the need for external equipment. The Axis M7001 (about $350 online) is an example of this style:
  • Desktop: Standalone encoders are available in a number of fixed port counts, typically 1 or 4 ports, though 2 and 8 port versions are sometimes available. Models such as these are intended to be desk or shelf-mounted, as they typically do not rack mount, though some models allow both rack or desktop use. Desktop models are often used when replacing a small camera count system, such a a 4- or 8-channel DVR replacement. Standalone encoders typically sell online for $400-$500 for a single-port model, to $800 or more for four-port versions.
  • Ruggedized: Rugged encoders are used in locations where mounting the encoder outdoors is preferred. Due to extended temperature and humidity ranges, ruggedized encoders may be installed without external climate controlled enclosures. Bosch has been perhaps the leading supplier of rugged encoders, with their VideoJet X series, available in multiple configurations, shown here:

    Axis also recently announced the Q7424-R rugged encoder, their first. Rugged encoders typically sell only for about $1,200 and up.

The main drawback to standalone encoders is that no additional ports may be added once installed. If more cameras are needed, an additional encoder must be added. In systems where expansion is planned, for instance when an analog camera takeover is phased in, chassis-based encoders are likely a better option.

Rack-Mount Encoders

Rack-mount encoders are preferred in higher-density applications, and available in both fixed and flexible channel counts using blade/chassis designs.

Fixed Channel Count

Fixed channel counts may simply be used whenever rack-mounting is preferred, but they especially make sense when replacing analog DVRs. For instance, a 16-channel DVR may be replaced with a 16-channel encoder, reducing the need to reroute wires in the rack, as they may simply be plugged into the encoder in place of the DVR. Fixed channel count rack-mount encoders are most often either 8 or 16 channels, though 24- and 32-channel models are not unheard of.

Fixed channel count encoder pricing varies widely, depending on featureset and channel count. However, most are typically in the range of $1,000-2,000.

Chassis-Based

In even higher-density applications, above 16 channels, chassis/blade models are available, in which encoder cards (blades), typically containing four ports, are installed in a multiple-slot chassis, such as this example by Sony:

Multiple slot counts are available, varying by manufacturer, but three-, four-, and twelve-slot models are not uncommon. This design allows the encoder's channel count to more closely match the camera count, as opposed to using 8- or 16-channel fixed channel encoders. Chassis-based encoders offer redundancy features which other models normally do not, such as multiple Ethernet ports and redundant power supplies for failover.

Chassis-based models vary widely in price depending on features. A four-slot Sony SNTRS1U chassis, for example, sells for about $450 online, while a 14-slot Axis Q7900, with dual power supplies sells for nearly $3,000. Blades also range in price, from about $600 to $1,400, depending on channel count and features.

The main drawback of using chassis/blade encoders is cost, as four four-channel blades plus a chassis may be more expensive than a fixed port count 16-channel model. However, if large quantities of cameras and redundancy are concerns, they're likely the best option.

Encoder Features

Encoder featuresets vary from manufacturer to manufacturer, and typically within a given manufacturer's line. This allows users to select an encoder which best matches their application, but care must be taken to ensure all features are covered. Common features which vary include:

  • Maximum framerate: While many encoders are capable of a full 30 FPS on all channels, many, especially lower-cost models, may have maximum frame rates of 15 FPS or below. Some models, the Vivotek VS8801 for example, may allow 30 FPS on individual channels, but a maximum total frame rate across all channels.
  • Image processing: Some encoders attempt to improve analog camera signals by applying image processing. These most often include contrast and color enhancements, or digital noise reduction. Other models do not include these features, simply encoding signal as-is.
  • PTZ control: RS-485/RS-422 outputs used for analog PTZ control are not included on all encoders. PTZ protocol support varies as well, with the majority supporting Pelco D, which many, if not most, PTZ cameras support. Less common PTZ protocols, such as Bosch biphase or coaxitron normally require external hardware be used.
  • I/O and audio: Low-cost encoders may not include audio or I/O. These functions are not applicable in many installations, but may be used with specialized cameras, such as video door intercoms, which we review in our door intercom tutorial.
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