Quality, Complexity, And Bit-rate Control For Video Coding

Multimedia is characterized by its video capability since video is the most efficient presentation method among various digital media signals. But digital video has an inherently high bandwidth, which limits the video application in multimedia services. To maximize the use of channel and storage, video signal need to be efficiently compressed. The increasing demand of video interoperability ignited ITU-T and ISO/IEC to develop lots of standards for video processing, transmitting and storing. Except H.264, almost all of the standards use MC-DPCM/DCT technologies. Motion compensation and DCT (discrete cosine transform) are used to decorrelate spatio-temporal correlation of video signal and quantization is used to exploit perceptual redundancy of nature video.Video coding can essentially be view as a multi-dimensional optimization problem; the key dimensions concerned in this problem are rate, quality, coding computational complexity, error resilience and memory size. In order to provide insights into common video system design problems, several issues for real-time video coding have been addressed in this dissertation, which are video coding computational complexity reduction, rate control, error control and error resilience.It is well known that video processing is the most computationally intensive part in multimedia computation. Real-time video coding previously resorted to dedicated hardware or professional equipments. With the development of general-purpose processors and high efficient algorithms, it is possible to implement a software-based real-time video encoder, and its low cost and easy upgradability attract developers' interests to migrate video encoding from dedicated hardware to more flexible software. In this paper, we first rearrange the encoder structure to support complexity scalability; then a lot of high performance algorithms are used on the key time-consuming modules in coding process; next, in programming level, processors characters are considered to improve data access efficiency and processing parallelism; finally, other programming methods, such as lookup table, explicitly assemble on key modules, are used to speed up coding process.Secondly, rate-distortion (R-D) analysis and rate control play an important role in video coding and communication systems, which are to prevent buffer malfunction and provide the highest possible video quality under the constraints of rate and delay. In conventional R-D analysis, the bitrate R and distortion D are considered as function of quantization parameter q, which are usually developed in pixel-domain or spatial domain. These source models either have high computational complexity or subject to relatively large estimation evaluation and control error. In this dissertation, a R-D analysis in DCT domain or compressed domain is developed, which can provide more accurate prediction for target bit allocation. Based on DCT domain R-D analysis, we provide a new constant bitrate (CBR) rate control algorithm, which can cure TM5 algorithm' two limitations, buffer conformance and scene cut problem. For variable bitrate (VBR) rate control, weproposed a single-pass VBR rate control algorithm for real-time video coding application. It doesn't require pre-analysis and multi-pass coding, and can achieve a constant video quality.Thirdly, in video communication system, transmission errors and packet losses are inevitable due to channels noise and network congestion. In contrast with data communications, which are not usually subject to strict delay constraints and can therefore be handled using network protocols that uses retransmission to ensure error-free delivery, real-time video is delay sensitive and cannot easily make use of retransmission. The extensive use of prediction and variable-length coding in video coding renders compressed bitstreams especially vulnerable to transmission errors and data losses. Based on detailed analyses of MC-DPCM/DCT mechanism, several error detection, resilience, concealment methods are discussed in this paper.