Consider the block-based video coding application of Digital Signal Processing: a) Illustrate the concept of block motion estimation in a video coder and explain its operation. [35%) b) Explain the difference in the methods used for differential motion vector coding in ITU-T H.261 and H.263 video coding standards. Comment on the error performance of both methods. [30%] c) A motion estimator is designed for the high-precision compression of an ultra high definition (UHD) video sequence with highly motion-active content. Analyse the main factors that should be considered in designing this motion estimator and comment on their impact on both the video coding performance and complexity. [35%)