vel down in the hierarchy is the picture (the primary coding unit of a video sequence). MPEG-2 only defines a slice (used to handle errors in a bit stream). Both MPEG-1 and MPEG-2 define a macroblock (a 16 pixel by 16 line selection of luminance components and its corresponding 8 pixel by 8 line chrominance components), and a block (an 8-pixel by 8-line set of luminance and chrominance values). MPEG-1 handles only two channels of audio. MPEG-2 handles up to five channels (surround sound). Because of this difference, MPEG-1 and MPEG-2 use different techniques to synchronize audio and video. In summary, MPEG-2 extends MPEG-1 to handle audiovisual broadcasts (whereas MPEG-1 was aimed at playback applications). It can deliver audiovisual material at higher speeds, with greater resolution, with surround sound audio and in interlaced scanned environments. MPEG-2 may eventually replace MPEG-1 but it was not intended to do SO. MPEG 4-ISO/IEC 14496 The official title of the ISO/IEC's MPEG-4 specification is, "Very Low Bitrate Audio- Visual Coding." It was approved as a Working Draft in November 1994, finalized in October 1998, and became an International Standard in 1999. MPEG-4 is targeted at low bit rate applications with frame sizes of 176x144 or less, frame rates of 10Hz or less, and encoded bit rates of 4.8-64 Kbps. The promise of MPEG Family of Specifications MPEG-4 is to provide fully backward compatible extensions under the title of MPEG- 4 Version 2. MPEG-4 is designed to address digital television, interactive graphics applications that build on synthetic content, and interactive multimedia (e.g., distribution of, and access to, content). MPEG-4 provides standardized technological elements to enable the integration of the production, distribution, and content access paradigms of these three domains. MPEG-4 enables extensive reusability of content across disparate technologies such as digital television, animated graphics, and World Wide Web (WWW) pages. It also offers manageability of content owner rights. Furth