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Scalable Video Coding: Another Kneecap Blown Away

February 13, 2014 | Telepresence Options


Story and images by Andrew Davis / No Jitter

Scalable video coding, or SVC, may be just the latest example of the video conferencing industry's affinity for never missing an opportunity to miss an opportunity. In this case we're talking about interoperability.

H.264 SVC, an algorithm for encoding/decoding video streams, became an internationally approved (ITU) standard (formally known as a Recommendation) in 2007--ancient history in today's UC world.

The details of SVC are outside the scope of this document. A video bitstream is called scalable if part of the stream can be removed in such a way that the resulting bitstream is still decodable. Suffice to note that H.264 SVC standardizes the encoding of a video bitstream into a base layer and one or more enhancement layers.

The enhancements add frame rate (temporal enhancements), image resolution (spatial enhancements), or image quality (signal-to-noise enhancements) to the base layer. The base layer itself complies with the old H.264 baseline profile, commonly (but inaccurately) referred to as H.264 AVC. This is an important detail.

SVC facilitates videoconferencing over best-effort IP networks like the Internet because when things get tough on the network, SVC can temporarily send just base layer packets. More to the point, a video switch/router in the middle of the connection (the video infrastructure that is so often overlooked in today's SVC debates) decides dynamically which layers to send to which endpoints, depending on the endpoint's processing power, network bandwidth, and traffic conditions. The switch does not perform any transcoding; since processor requirements are minimal, this fundamentally changes the economics of multipoint video calls.

This type of architecture is a natural for calls that connect high-performance room systems with desktops on a LAN and/or mobile devices on a cellular network or slow Internet pipe.

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