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Motion Estimation algorithm is one of the important issues in video coding standards such as ISO MPEG-1/2 and ITU-T H.263. These international standards regularly use a conventional Full Search (FS) Algorithm to estimate the motion of pixels between pairs of image blocks. Since a FS method requires intensive computations and the distortion function needs to be evaluated many times for each target block. the process is very time consuming. To alleviate this acute problem, new search algorithms, Orthogonal Logarithmic Search (OLS) and Diagonal Logarithmic Search (DLS), have been designed and implemented. The performance of the algorithms are evaluated by using standard 176x 144 pixels quarter common intermediate format (QCIF) benchmark video sequences and the results are compared to the traditional well-known FS Algorithm and a widely used fast search algorithm called the Three Step Search (3SS), The fast search algorithms are known as sub-optimal algorithms as they test only some of the candidate blocks from the search area and choose a match from a subset of blocks. These algorithms can reduce the computational complexity as they do not examine all candidate blocks and hence are algorithmically faster. However, the quality is generally not as good as that of the FS algorithms but can be acceptable in terms of subjective quality. The important metrics, time and Peak Signal to Noise Ratio are used to evaluate the novel algorithms. The results show that the strength of the algorithms lie in their speed of operation as they are much faster than the FS and 3SS. The performance in speed is improved by 85.37% and 22% over the FS and 3SS respectively for the OLS. For the DLS, the speed advantages are 88.77% and 40% over the FS and 3SS. Furthermore, the accuracy of prediction of OLS and DLS are comparahle to the 3SS.

The delivery of high quality video to wireless users depends on achieving high compression efficiency and high robustness to wireless channel errors. Research on these topics has led to the introduction of a number of video codec standards. However, most of these standards incorporate redundant syntactical information that renders the video more susceptible to channel errors, and reduces the compression efficiency. This thesis presents a new approach to video compression that removes most of the problems associated with the excess syntax, a header compressor and decompressor is placed adjacent to encoder and decoder respectively. The compressor removes the excess header redundancy and decompressor regenerates the original header using already stored reference. The thesis investigates the syntactical header information of video coding standards MPEG-4 and H.264. The analysis shows that the overheads in small video packet may contribute up to 50% of the texture data. The video packet header fields are classified as static and dynamic. Based on the header analysis, a comprehensive header compression scheme is designed for MPEG-4 and H.264 video packets. For a practical scenario, simulations of video packets are carried out including the compressed IP/UDP/RTP overheads. The ROHC (RObust Header Compression) standard compresses the IP/UDP/RTP headers. In this thesis, ROHC parameters have been optimised for transmission over 3GPP simulated downlink channel. Furthermore, an improvement in the ROHC U-mode has been proposed to reduce the effects of unnecessary packet loss due to false context damage. Results show better video quality and lower packet loss rates with proposed scheme. The efficiency of the proposed video header compression scheme is evaluated with different combinations of encoding parameters. Experiments show the using the proposed video header compression scheme, up to 95% of header redundancy may be removed. Extensive simulations illustrate improvements in video quality due to the proposed header compression scheme under various channel conditions. The video quality is further enhanced by using a header-compression based unequal error protection scheme. The bits saved due to header compression can be utilised adaptively to protect the critical data at a fixed transmission rate. The results show significant improvement in objective and subjective video quality.

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