智慧型手機與平板電腦的蓬勃發展帶動了一波行動通信的革命，特別是實現了在各種不同的行動裝置上的播放行動視訊的應用。而支援多屏幕的技術也是目前一項促進行動視訊應用的最熱門的技術之一，如何使得高畫質的電視節目、影片或是電影可以快速且無縫的在各種不同尺寸的顯示裝置上播放是一個正在研究發展的技術。由於一般H.264解析度轉換編碼需要很複雜的運算來將一個H.264的視訊位元流解碼後將其轉換到不同的解析度後再進行編碼成H.264的視訊。尤其是當要執行高解析度的視訊節目與影片的降解析度轉換編碼，轉換編碼的時間會更延長。 本篇的論文就是要利用高解析度視訊畫面與低解析度視訊畫面之間的特性與相關性來提出一套非二冪次解析度轉換編碼的快速模式決策的演算法，來減少H.264轉換編碼的複雜度以加速編碼的時間。這個演算法是利用位置相關性來將進行縮減轉換編碼時間的。換言之，就是分析在低解析度視訊中的區塊對應到高解析度視訊中的相對應的位置的關聯性，以此資訊來做判斷是否要省略下一層的子巨區塊模式的執行。而且也會利用高解析度視訊上面的區塊編碼資訊來決定是否只執行巨區塊的模式決策而已。 經過將這一快速演算法模擬在H.264 JM15.1版程式當中所得到的結果顯示，可以得到明顯的時間改善，同時影像視訊的品質也可以保持幾乎不變。 The rapid growth of smart phones and tablets bring the revolution of mobile communication, especially mobile video applications played on all sorts of mobile devices. The technology for multi-screen supporting is one of the top issues in promoting mobile video applications. How to play TV programs, video clips, and movies on different display devices with fast transcoding speed and flawless playback is under developing. The conventional H.264 resolution transcoding that decodes an H.264 bit stream and re-encodes it to a different resolution needs a large amount of processing power. In particular, the processing time is increasing when downsizing transcoding is processed on the high resolution video. The objective of this work is to develop a fast mode decision algorithm for non-dyadic resolution transcoding. It is based on the feature and correlation between the high and low resolution videos to reduce the complexity of the H.264 transcoding. This algorithm is location dependent. Namely, the corresponding area in the high resolution video to a low resolution block is analyzed and the relationship can be used to determine if some of the sub-macro block modes can be skipped. And the mode information of the macro block in high resolution video can be used to determine if only the macro block modes of the low resolution video are performed. The experimental results running under JM15.1 reference software show that the proposed algorithm can reduce the transcoding time significantly while keeping the video quality.
