在一般的視訊編碼中，在位元率失真成本最佳化 (Rate Distortion Optimization)過程中通常利用拉格朗日參數 (Lagrange Multiplier)來權衡位元率與失真量並計算出位元率失真成本 (Rate Distortion Cost)並找到最合適的編碼模式。然而量化參數(Quantization Parameter)必須事先決定，這往往不是最好的。在本論文中，我們首先提出一個基於固定Lagrange Multiplier的2-Pass編碼位元率控制(Rate Control)方法。透過Pass-1編碼後可以預測出一個精確的Lagrange Multiplier，並在Pass-2編碼中採用它做為一個固定參數。在優化過後，我們提出了1-Pass編碼位元率控制方法，不僅保持了影像品質而且還降低了計算複雜度。實驗結果顯示，相對於實現JVT-G012的H.264/AVC參考軟體JM13.2，我們提出的2-Pass編碼方法與1-Pass編碼方法兩者皆大大的提高影像品質。此外還提出了優化程序，以減少計算複雜度和準確控制位元率。

In general video coding, the process of Rate Distortion Optimization (RDO) usually utilizes the Rate-Distortion (R-D) cost function involving the Lagrange multiplier to weight the ratio between bit rates and distortions to find the most suitable encoding mode. However, the quantization parameter (QP) has to be decided in advance, which is often not the best one. In this thesis, at first we propose a two-pass rate control (RC) mechanism based on a fixed Lagrange multiplier. An accurate lambda value is estimated after the first pass coding, so that it can be adopted as a fixed parameter in the second pass coding. After optimization, we proposed the one-pass RC scheme not only keep the video quality performance but also reduce the computational complexity. Experiment results show that, compared to the JVG-G012 method implemented in H.264/AVC reference software JM13.2, both the proposed two-pass and one-pass method could significantly improve the video quality. Besides, a proposed optimum procedure is also presented to reduce the computational complexity and accurately controls the bit rate.

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