臺灣博碩士論文加值系統

新興的H.264 壓縮標準中，採用更複雜且精確的編碼方式，提供更低的位元率和
更好的視訊品質。因此運用H.264 的編碼特性，來進行任意畫面縮小的視訊轉換
編碼，將原始的大視訊畫面縮小轉換成符合使用者系統裝置的視訊畫面，進而滿
足使用者的需求。為了節省轉換編碼器的運算複雜度，本文提出了模式決策與移
動向量合成演算法，用來減少轉換編碼過程中重複編碼的運算複雜度。此演算法
運用整數編碼所得到的非零值個數，作為模式決策的參考條件，進而決定出縮小
畫面後巨區塊的編碼模式。之後，對於模式決策的結果，給予合適的移動向量。
在移動向量合成演算法中，延續使用非零值個數，再運用畫面縮小後之區塊與原
始畫面相關區塊間所覆蓋的面積，來合成移動向量。在實驗結果中，使用模式決
策與移動向量合成演算法所需執行的編碼時間遠小於其他任意縮小畫面的轉換
編碼法。在客觀品質比較中，與其他的轉換編碼法只有些微的差距。比較主觀品
質，我們所提出的演算法與其他轉換編碼法的視訊品質相差無幾。由此，本論文
中在容許些微的客觀品質結果下降，換取較快的編碼速度，也維持視訊畫面原有
的主觀品質，而達到提升H.264 轉換編碼器的運算效能。

Video transcoder is an important intermediary between the emerging applications.
One of the aims of the transcoder is for the different display resolutions. In the new
video coding standard H.264/AVC, the goal is to enhance compression performance at
the lower bitrates environment. Compared with the prior video coding standards,
H.264 adopts new coding schemes like variable block sizes, multiple reference frames,
4×4 integer transform coding and rate distortion optimization (RDO). For the encoder
in the transcoder, new schemes incur more computational complexity. To avoid the
problem occurs in the encoder of the transcoder, the mode decision and motion vector
composition algorithms are proposed. Our scheme for mode decision employs
non-zero coefficient number of related blocks to determine the modes for downscaled
macroblocks. The motion vector composition adopts the maximum area and non-zero
coefficients in the covered region between original blocks and downscaled blocks to
composite the new motion vector for the downscaled macroblock. The proposed
algorithms not only reduce the computational complexity but also keep video quality
in the transcoder.

Contents

Chapter 1 Introduction 1
1.1 Overview of the Video Transcoding 1
1.2 Overview of the H.264/AVC Video Coding Standard 8
1.3 Motivation 15
1.4 Organization of the Thesis 15
Chapter 2 Review of Related Downscaling Video Transcoding 16
2.1 Overview of the Downscaling Processing 16
2.2 Mode Mapping Method for H.264/AVC Spatial Downscaling Transcoding ‎[13] 20
2.3 Arbitrary Downsizing Video Transcoding using H.26L Standard ‎[15] 24
2.4 Fast Motion Re-Estimation for Arbitrary Downsizing Video Transcoding using H.264/AVC Standard ‎[16] 28
Chapter 3 Proposed Arbitrary Downscaling Video Transcoding Algorithm 31
3.1 The Mode Decision Algorithm 34
3.1.1 INTRA Mode Decision 36
3.1.2 INTER Mode Decision 39
3.2 The Motion Vector Composition Algorithm 44
Chapter 4 Experimental Results and Performance Analysis 53
4.1 Parameter Setting 55
4.2 PSNR Comparison 56
4.3 The Encoding Time Comparison 63
4.4 Comparison of the Subjective Quality 70
Chapter 5 Conclusion and Future Work 80
Bibliography 83

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