ession applications using its services. In order to meet these standards have been developed by the International requirements MPEG-7 has created a hierarchic frame- Standardization Organization (ISO), the International work that can handle many levels of description. In Video compression CHAPTER addition other types of descriptive data are defined, such 2. H.230 - Defines frame control signals for audio as, coding formats, data access conditions, parental rat- visual systems. ings, relevant links, and the overall context. MPEG-7 is made up of three main elements that include description 3. H.242 - Defines audiovisual communications proto- col for channels supporting up to 2 Mbps. tools, storage and transmission system tools, and a lan- guage to define the MPEG-7 syntax. These elements 4. H.261 - Defines the video encoder/decoder for au- provide the flexibility to meet the stated requirements. diovisual services at p X 64 kbps. Work on the latest MPEG standard began in 2000. It 5. H.320 - Defines narrow-band audiovisual terminal was started as an extension to MPEG-7 and is known as equipment for p X 64 kbps transmission. MPEG-21 (ISO/IEC 21000). It is focused on defining the common content and user access model addressing the vast proliferation of new and old multimedia distri- bution and reception technologies. MPEG-21 specifically The H.261 encoder block diagrams are depicted in looks to define the technology needed to support users to Fig. 7.4-8 (a) and (b). An H.261 source coder imple- exchange, access, consume, trade, and otherwise ma- mentation is depicted in (c). The source coder imple- nipulate Digital items in an efficient, transparent and ments the video encoding algorithm that includes the interoperable way. Digital items are defined to be the spatial encoder, the quantizer, the temporal prediction fundamental unit of distribution and transaction, i.e., encoder, and the VLC. The spatial encoder is defined to content (Web page, picture, movie, etc.). use the two dimensional 8 X 8 pixel block DCT and The