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Scalable video coding (SVC) and transmission has been a research topic for many years. Among other objectives, it aims to support different receiving devices, perhaps connected through a heterogeneous network structure, using a single bit stream. Earlier attempts of standardized scalable video coding, for example in MPEG-2, H.263, or MPEG-4 Visual, have not been commercially successful. Nevertheless, the Joint Video Team has recently focused on the development of the scalable video extensions of H.264/AVC, known as SVC. Some of the key problems of older scalable compression techniques have been solved in SVC and, at the same time, new and compelling use cases for SVC have been identified. While it is certainly important to develop coding tools targeted at high coding efficiency, the design of the features of the interface between the core coding technologies and the system and transport are also of vital importance for the success of SVC. Only through this interface, and novel mechanisms defined therein, applications can take advantage of the scalability features of the coded video signal. This paper provides an overview of the system interface features defined in the SVC specification. We discuss, amongst other features, bit stream structure, extended network abstraction layer (NAL) unit header, and supplemental enhancement information (SEI) messages related to scalability information.