在本篇論文中，我們提出二步模式決策(Two-stage mode decision)演算法以及降低小數像素移動估測計算(Sub-pixel motion estimation Reduction)兩種方法來加速視訊壓縮標準H.264/AVC的執行時間，在有使用位元率失真比最佳化(Rate distortion optimization)的情況下。由於在使用壓縮量失真比最佳化時，更多的計算量必需被投入來取得在特定的壓縮比條件下最小的失真使得該方法難以應用在活動式或是嵌入式的系統上。二步模式決策被提出來減少計算的時間但同時仍保持高原有的高品質，它包含兩個步驟：第一步運用先前壓縮完成的畫面資訊來預測模式。第二步則使用貝式機率法則和倒傳遞類神經網路做進一步的選擇。此外小數像素移動估測在H.264/AVC編碼流程中也是一個相當花費時間以及記憶體的動作。忽略小數像素移動估測被提出來決定小數像素移動估測是否需要執行，這是根據整數像素移動估測中取得的最佳位置及其週遭位置來決定。根據實驗結果，二步模式決策在損失少部分的影像品質以及壓縮比的條件下減少超過一半的計算時間。忽略小數像素移動估測同樣減少了計算的時間也僅伴隨著少量的損耗。此二演算法相較於原始的H.264/AVC標準提供在相似品質之下更快速的壓縮。

　　In this paper we proposed a two-stage mode decision (TSMD) algorithm and Sub-pixel motion estimation reduction (SMER) method to speed up the execution of the H.264/AVC video encoding with rate distortion optimization (RDO). Because much more computation power is required to achieve the minimal distortion for a given bit-rate budget by RDO algorithm, it is difficult to apply H.264 in mobile devices or embedded systems. The proposed TSMD algorithm is proposed to reduce the computation time with high quality video encoding. It is including two stages: The first stage is to predict the possible encoding modes according to the previous frame’s information. The second stage is to apply the refinement mode utilizing Baye's probability rule and Back-Propagation neural network (BPN). Moreover, the sub-pixel motion estimation is also a time and memory consuming operation during the H.264/AVC encoding procedure. The SMER method is proposed to decide whether the sub-pixel motion estimation can be skipped by using the relation among the pixels around the best position after the integer-pixel motion estimation is finished. According to the experiment results, over 50% of the computation time is reduced with a slightly loss in peak signal-to-noise ratio (PSNR) and a slightly increment in bit rate when TSMD is applied. The computation time is further reduced by the SMER method with little reduction of the PSNR. These two algorithms provide faster encoding with close compression performance compared with the H.264/AVC standard reference software (JM 9.2).

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