H.264相較於以往的視訊標準，在壓縮效能上有很明顯的改進，然而所付出的代價即為造成編碼端複雜度的大量提升，以及增加硬體實現的困難度；而其計算的複雜度主要分布在可變區塊大小與多幅參考畫面機制下的移動預估計算。 為了讓H.264能達到即時應用的目標，本論文提出了快速橫向線型移動預估機制並實現於Equator DSP。快速橫向線型移動預估機制主要可分成兩部分－橫向線型搜尋演算法與整合可變區塊大小和多幅參考畫面的快速決策機制，橫向線型搜尋演算法利用Equator提供的128-bit暫存器架構來同時加速SAD計算與資料搬移。除此之外，我們在橫向線型搜尋演算法中也使用固定搜尋視窗來進一步降低SAD的計算量。在可變區塊大小演算法裡，我們提出了三階層的決策法則來省略不必要的移動預估計算量，另一方面我們也在多幅參考畫面演算法中使用快速中斷的決策方式來降低更多的計算量。由實驗結果可得知，我們於Equator上實現所提出的快速橫向線型移動預估機制，能使得執行移動預估計算量的時脈數大幅降低至98%，而不會造成視訊品質的大量失真。 H.264 video coding standard can achieve considerably higher coding efficiency than previous standards. However, this comes at a cost in considerably increased complexity at the encoder and thus increases the difficulty in hardware implementation. The computation complexity is mainly due to motion estimation in combination of variable block sizes and multi-reference frames. To achieve the objective of real-time applications, we propose a fast multiple decision horizontal line search (MDHLS) scheme for H.264 and implement it on Equator DSP. The MDHLS mainly contains two parts, one is HLS algorithm and the other is a fast decision scheme for variable block sizes and multi-reference frames. HLS utilizes the 128-bit register of Equator to jointly accelerate SAD calculation and data access. And we employ a fixed search window size in HLS for further reducing SAD calculation. The proposed variable block size algorithm provides a three-stage decision rule to remove unnecessary computations of motion estimation. An early termination decision rule is also developed for multi-reference frame algorithm. Simulation results show MDHLS can achieve up to 98% cycle reduction in motion estimation implemented on Equator DSP and the coding efficiency is only slightly decreased.
