The videoconferencing applications transmit video and audio data through data networks. The current networks such as the Internet are heterogeneous: their subnets may possess di erent bandwidths. When a videoconference covers subnets of di erent bandwidths, multiple video coding schemes of di erent bandwidth requirements can be used at the same time to make good use of the bandwidth resources. ...

(IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." To learn the ...

A comparative study of arbitrarily programmable, but xed-rate videophone codecs using quarter common intermediate format (QCIF) video sequences scanned at 10 frames/s is ooered. In contrast to existing and forthcoming standard schemes, such as the H.261, H.263 and MPEG2, MPEG4 codecs, which rely on bandwidth-eecient but error-sensitive variable-length coding techniques combined with a complex s...

The most important issue in video encoding is motion compensation within a frame sequence. Block matching techniques are used by various algorithms [5], [6] to estimate the motion into succesive frames. Full search 2D block matching is the most widely used algorithm for video encoding in all standards (H261, MPEG1-2 , HTDV etc). It provides with the best SNR, since it uses exhaustive search to ...

Current proposals for the catalytic mechanism of aspartic proteinases are largely based on X-ray structures of bound oligopeptide inhibitors possessing nonhydrolyzable analogues of the scissile peptide bond. However, the positions of protons on the catalytic aspartates and the ligand in these complexes have not been determined with certainty. Thus, our objective was to locate crucial protons at...