Video transcoding for multimedia communication networks.

Video transcoding is a generic name for a video gateway structure whereby the tandeming process does not involve any high complexity cascaded decoding and re-encoding operations in contrast to the existing conventional solutions. Diverse multimedia communication network characteristics, such as bandwidth limitations and varying congestion conditions, incur quality degradation in video transmissions. The matching of input and output network constraints and characteristics is possible with video transcoding at a centralised unit within the network. Moreover, video transcoding also provides a suitable translation mechanism for different video compression standards achieving a transparent interconnection between diverse network topologies. In addition, video transcoding offers a method for providing robustness against transmission error effects which occur during the transmission of compressed video streams over highly bandwidth- restricted communication media, such as popular mobile-wireless networks. Due to the severe bandwidth restrictions of such networks, the video signals require low bit rate coding which in turn renders video streams highly susceptible to radio channel errors. Therefore, error-resilient operations also need to be provided together with the syntax and transmission rate translation features of video transcoders. The unique features of video transcoding provide flexible and efficient ways to alleviate the previously addressed three major issues for various requirements. These requirements can be imposed by the diversity of networks on which numerous applications are running or by different standards themselves as well as by a wide range of users. This is strictly related to a universal interoperability issue of heterogeneous characteristics and requirements which demand effective end-to-end solutions. Thus, the aim of this research presented in this thesis is to develop algorithms for the provision of such remedial solutions to the interoperability problem. In the light of these facts, the research work focuses on the design of various video transcoding algorithms. The objectives of these algorithms are to ease network congestion and/or user bandwidth limitation conditions, support essential standard conversions between different compression schemes and provide necessary error robustness over highly error-prone transmission media, such as mobile radio networks. The ultimate target is to establish a common platform where all the above three aims are successfully satisfied. Extensive computer simulations demonstrate the effectiveness of the proposed and designed systems, throughout the course of the research work. These simulations are assessed with the use of objective and subjective performance measures