alized in 2000 and produced a standardized description of the mul- timedia. An ability to describe the content facilitates efficient searching and browsing. The standard does not code video but rather describes it. MPEG-7 is formally called the Multi- media Content Description Interface. MPEG-21 defines a standard for permissions and digital rights for audio and video content. It contains machine-readable license information. The numbering of the MPEG standards remains an enigma, with various stories associated with the missing numbers. However, no clear pattern emerges. H.26x The H.261 standard was published by the CCITT (now ITU-T) and was designed for vid- eoconferencing and videophone applications over ISDN telephone lines. It has traditionally utilized 64-kbit/s baseline ISDN and uses multiples of 64 kbit/s (ITU-T, 1993). Buffering is used to smooth out variations in bitrate generated by the video encoder; to achieve a con- stant bitrate, a simple feedback loop is employed to report on the state of the buffer to the encoder. If the buffer becomes too full, the quantization scale factor is increased to reduce the data at the expense of video quality. The coding technique in H.261 removes temporal redundancy by interframe prediction, and spatial redundancy by transform coding. There are no B frames, and motion compensa- tion is optional; the codec makes a decision whether to inter- or intracode macroblocks. H.261 defines two resolutions, 352 X 288 and 176 X 144, commonly known as CIF and QCIF formats, respectively. H.263 was published by ITU-T and was particularly aimed at coding video for low bitrates (typically 20-30 kbit/s) (ITU-T, 1998). The H.263 standard is based on techniques common to many current video-coding standards: interpicture prediction to utilize temporal Compression Overview redundancy and transform coding to reduce spatial redundancy. Motion compensation is based on one motion vector per macroblock, coded with half-pixel precision, and the decoder has motion compensation capability. The H.26