vel multimedia applications, including object-oriented coding, virtual-reality mod- eling, user graphic interactivity, computer-generated video and audio, and digital rights management and protection. The MPEG-4 audio codec, which is described in Part 3, is referred to as advanced audio coding (AAC).4 47 The key intent of AAC is to provide better sound compression without affecting quality, or better quality with a given stream rate. The claim is that in sound quality a 48 kbit/s AAC stream would outperform a 128 kbit/s MP3 stream, while the consensus concerns more the AAC superiority over any other 32-64 kbit/s audio codec, and its improved compression with respect to MP3. The MPEG-4 video codecs are described in Part 2 and Part 10. The first (Part 2) concerns image compression through DCT in view of the simplest implementation "profiles," see further. The second (Part 10), is also referred to as H.264 (the ITU-T denomination) or advanced video coding (AVC). 48 The key intent of this advanced codec is to reduce the bit rate without affecting the picture's end quality. This is enabled by several feature, of which only a few can be mentioned or make sense within the scope of this overview. For instance, inter-picture prediction is not limited to B-frames (as in MPEG-2) but up to 32 neighboring reference frames. A variable macroblock size ranging from 4 X 4 16 X 16 enables more precise mapping and tracking of moving regions in still back- grounds. Compression is introduced by context-adaptive binary arithmetic coding and variable-length (Huffman) coding (Chapter 10), referred to as CABAC and CAVLC, 44 See, for instance: http://en.wikipedia.org/wiki/DVD. 45 See, for instance: http://en.wikipedia.org/wiki/DVD_Formats. 46 See, for instance: http://en.wikipedia.org/wiki/MPEG-4; www.chiariglione.org/mpeg/standards/mpeg-4/ mpeg-4.htm; www.apple.com/quicktime/technologies/mpeg4/. 47 See, for instance: http://en.wikipedia.org/wiki/MPEG-4_Part_3; www.mpeg.org. 48 See, for instance: http://en.wikipedia.org/wiki/H.264. Append