|Author:||Chung, Yuen-lun Charles|
|Title:||Compressed video transmission with variable bit-rate|
Data transmission systems
Hong Kong Polytechnic University -- Dissertations
Department of Electronic Engineering
|Pages:||iv, 97,  leaves : ill. ; 30 cm|
|Abstract:||During the past few years, increasing demands of multimedia and hypermedia services have rapidly boosted the development of the information super-highway, the Internet. Users of the service always wish to obtain all forms of information(audio, video) in the shortest time and from everywhere around the world. Nowadays, the explosive growth of the number of users and the data volume required per user pose a big challenge for developers to cope with. In general, there are two approaches to get around the problem. The first one is to increase the capacity of the transmission network and the second one is to control the data volume per user dumped into the network. The latter simply means data compression. This dissertation basically deals with compressed video transmission with variable output bit-rate. It involves the studies in a number of areas; video compression, bit-rate control and data transmission. In the beginning of the dissertation, general problems and solutions in the related areas are discussed. Basically, the studies of video compression is confined to the MPEG-1 specification. In particular, the bit-rate control here is actually achieved by varying the intra-frame and inter-frame quantization factors and re-arranging the frame types defined in the MPEG-1 specification. In fact, through the variations of these parameters, trade-off between picture quality and output bit-rate can be achieved. Analytical results show that different combinations of the quantization factors must be selected for the video with different levels of motions in order to obtain optimal performance. As a result, classification of video must be performed. In terms of implementation, a MS-Windows based program, the VDO system, has been developed for the evaluation of the effects of varying the compression parameters on output bit-rate and picture quality. The VDO system is based on the programs developed in some other final year projects from the Electronic Engineering Department. The old programs run under MS-DOS environment and support transmission of compressed video with the limited frame size of 80x80. In contrast to the old programs, the VDO system possesses significant improvements in various aspects. For networking capability, a set of new routines are written for connection management and for handling the unexpected network events gracefully. For performance, maximum frame size of 160x160 and changing the compression parameters in run-time are supported. Besides, the design philosophy of the VDO system is based on the concept of modular programming so that on one hand, it enables the evaluation of compression parameter changes; on the other hand, it serves as a platform for further studies on other new video compression and bit-rate control algorithms. However, there are still some possible improvements to VDO system itself. On compression algorithm side, when decoding the bit stream from the network, the bit pattern matching algorithm takes significant amount of time therefore a more efficient algorithm can be developed. On programming side, multi-threaded programming can improve the overall efficiency of the VDO system. The implementation of these is beyond the scope of this dissertation, future development may consider these enhancements.|
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