本論文旨在於研究適用於H.264/AVC視訊標準的快速外框模式決策演算法，目的在降低外框移動之估計運算量，並同時保持原有之編碼效能。在尋找最佳編碼的過程中，編碼器針對每一個搜尋點計算各種區塊尺寸所需要的編碼成本，是故大部分的編碼運算量集中在移動估計的程序上。在物體在極短時間之線性移動特性下，本決策演算法利用已編碼區塊之分析結果，加以判斷欲編碼區塊之同異質性，進而節省大部分的模式成本運算量。此外，本決策演算法亦利用時間和空間之模式關連性，節省不必要模式之成本計算。研究模擬結果顯示，本決策演算法節省之計算複雜度平均為原來編碼器所需要的65%，且進一步發現適用於各種類型之視訊影像。雖然在相同的bit rate下，PSNR至多下降0.1 dB，然而此一程度之品質衰減人類視覺無法察覺，因此可被忽略。

This thesis proposes a fast algorithm for inter mode decision in H.264/AVC to reducethe computational complexity while maintaining video quality. The major complexity domination in the H.264/AVC encoder is motion estimation. Motion estimator finds the best match by checking all possible block sizes and searching positions. Due to the regular motion of objects in a short time period, the proposed algorithm analyzes the information of motion and block sizes already encoded in the previous frames. Based on the analysis results, the current macroblock is classified as a homogenous or heterogeneous region to improve the motion estimation performance by reducing the candidate modes. This proposed algorithm also adopts the correlations in both spatial and temporal domains to further eliminate the unessential modes. Simulation results show that the proposed algorithm is suitable for different types of sequences. The design provides good performance about 70% of computational complexity saving at the expense of 0.03 dB PSNR degradation and 1% bit rate increment on average.

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