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We propose a fast transcoder from digital video (DV) to MPEG-4 in the coded domain. Since DV is interlaced sequence whereas MPEG-4 (SIF) is progressive sequence and different discrete cosine transform (DCT) mode (2 * 4 * 8DCT) is used in DV, different compressed domain transcoding method from that of MPEG to MPEG conversion is required. We have exploited matrix conversion reflecting these properties and introduce approximation and integration of resolution conversion and quantization process. Simulation results of DV to MPEG-4 conversion show that the proposed method can achieve very fast conversion while maintaining high transcoding performance when compared with baseband transcoding and siginificant improvement over conventional method is also realized. Index Terms--Compressed domain processing, discrete cosine transform (DCT), digital video (DV), MPEG-4, resolution conversion, transcoding.

An efficient technique for obtaining a variable length code (VLC) resistant to synchronization loss due to channel errors is proposed. Bit errors in the channel lead to incorrect decoding of a VLC and result in error states for continuous codewords. In this paper first a precise value is found for assessing the ability of a VLC to recover synchronization from the error states. Next a new transformation for converting a code into another of the same efficiency (equivalent transformation) is introduced, and several VLCs with an identical efficiency are compared through estimation of synchronization recovery in order to find an error-resistant VLC. Based on the equivalent transformation, an efficient method for finding an error-resistant VLC with high recovery performance from among multiple VLCs is described.

This paper first addresses integration of video services and expresses the view that various types of end-to-end QOS for video communications, ranging from videophone to high-definition television (HDTV), should be supported to utilize both broadband integrated services digital network (B-ISDN) services and video data. End-to-end QOS is recognized as a function of terminal capability and network performance. The key feature of B-ISDN is that both terminal capability and network performance are selectable and controllable. In order to capture the basic characteristics of end-to-end QOS, it is necessary to conduct experiments using a prototype system. We present a prototype system comprised of an ATM switch and video codecs. The ATM switch is based on distributed-memory-switch architecture, and it will provide for nonblocking cell-switching capability with a very low cell-transfer delay. Developed codecs conform to H.261 with an additional function of controlling average coding bit rate. We choose coding bit rate as a parameter of terminal capability and cell-loss ratio as a parameter of network performance. From experiments using a prototype system, a relationship between coding bit rate and cell-loss ratio was obtained.