H.264/AVC 具有非常高的編碼效率，主要因素為進行畫面間預 測編碼時，H.264 使用了七種不同的區塊大小來進行移動補償 (Motion Compensation)，同時又可參考多幅畫面，因此其編碼過程中 之計算複雜度較以往的視訊編碼標準高出數倍，故近年來有許多的研 究致力於發展H.264 快速演算法。 由於硬體對外部記憶體之存取頻寬有限，由參考文獻中可知，若 採用階層式取樣架構，並將硬體可平行處理的特性加入考慮，即可有 效降低處理高解析視訊所需之頻寬，如何在此架構及條件下兼顧畫面 品質以及位元率來加速演算法為本研究之主要目標。 本論文提出一套可在資源有限之硬體上壓縮高解析視訊畫面的 階層式H.264 移動估測快速演算法，在空間域上利用階層式的搜尋方 式減少搜尋點數，於時間域上利用線性移動動量模型(Linear Motion Model)的假設以減少搜尋範圍，同時在空間域及時間域上進行加速， 實驗結果顯示，整體運算複雜度最低可達到原始JM 12.4 的1.80%， 且只犧牲了0.10dB 的視訊品質。 H.264 advanced video coding exhibits much higher coding gain as well as computational complexity than previous video coding standards due to the utilization of coding tools such as variable block size and multi-reference frame in motion compensation process. There exist plenty of research outcomes that focus on the development of H.264 fast algorithms. The limited bandwidth during the access between hardware components and the external memory often becomes the bottleneck of the system performance. One of the solutions of encoding the high-definition video in hardware with limited resources is to employ a hierarchical subsampling structure with the parallel-processing hardware architecture. The main objective of this work is to maintain both the video quality and bit-rate while pursuing the gain from computational complexity reduction. This thesis proposes a hierarchical H.264 fast motion estimation algorithm by decreasing the coding complexity in both spatial and temporal domains. In spatial domain, we utilize the hierarchical search method to decrease the search points. In temporal domain, we utilize the linear motion model to reduce the search range. The simulation results show that the proposed algorithm can reduce the computational complexity to as low as 1.80% compared to JM12.4 with less than 0.10dB video quality degradation.
