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Fredrik Nilsson is general manager of Axis Communications' in the Americas and author of the definitive book on networked video surveillance, titled "Intelligent Network Video."

Video encoders come in a variety of sizes ranging from single-channel to 84-channel rack-based solutions.

Enhancing analog cameras with advanced IP-based abilities
Video encoders provide a multitude of advanced functions that can enable analog cameras in a hybrid system to support many of the features and functions otherwise limited to network cameras. For instance, many video encoders offer pan/tilt/zoom (PTZ) control so that a user can redirect an analog PTZ camera over the network by moving a computer mouse or joystick.

Power over Ethernet (PoE). If the video encoder supports PoE, both the encoder and the analog camera connected to it may receive power through the same cable used for data transmission. This provides substantial savings because it avoids the cost of installing separate power cables.

Image quality. Some video encoders support image fine-tuning as well as aspect ratio correction to avoid image distortion when viewed on a PC screen. High-performance video encoders deliver full frame rate (30 fps in NTSC and 25 fps in PAL) in all resolutions for all video channels. Furthermore, unlike analog transmissions, digital images retain their quality regardless of the distance the signal needs to travel.

Multi-stream capabilities. Some higher-end encoders have the ability to provide multi-stream encoding for each channel. For example, you can create two different compression and resolution streams for a single analog camera's transmission. One stream of a few frames per second could be sent for remote archiving while a full-frame-rate, high-resolution stream could be stored locally.

Other innovative features. A video encoder can provide video motion detection to all the attached cameras as well as camera tampering alarms, event management and integrated audio support. The technology also provides a foundation for more intelligent video features such as license plate recognition, people counting and other analytics.