多媒體是現在當紅的領域。從各種商品的出現(如MP3, 數位電視等)及流行，各種影像的編碼格式也成了一個重要的話題。在這個網路發達的時代，當不同的平台要相互溝通時，編碼需要一些相對應的轉換以應付不同的編碼標準。H.263到H.264的轉碼是目前一個新起且快速發展的領域。當許多線上軟體(如網路電話、線上會議系統)將編碼從H.263升級到H.264時，這兩種編碼間的轉換越來越重要。在目前的H.263到H.264轉碼中，許多架構提出不同的想法。然而這些架構所考量的範圍都過於狹小，對於影像品質及複雜度並無法達到最佳的平衡。在我們所推出的系統(MDPP, modified decoding parameter propagation architecture)中，除了對複雜度的降低外，對影像品質也能達到一定的水準。在架構中，除了對解出來的參數充分利用外，另外兩階段的MV搜尋機制更使得影像模式能夠正確的偵測。從實驗結果中我們可以發現，複雜度比起reference架構少了99%；另外平均上來說我們的架構比起支援多種模式的架構快上5~8倍。在速度快的情況下，RD曲線圖顯示我們的架構能達到近乎reference架構的影像品質，而且在不同的影像下皆有不錯的表現。由這些實驗結果，我們相信提出來的架構能夠在影像品質及複雜度上取得最好的平衡。 Transcoding from H.263 to H.264 is a rising topic recently when various applications(such as video phone, online conference) upgrade their systems from H.263 to H.264.Recently, several architectures for low complexity H.263 to H.264 transcoder are provided. However, trading between performance and complexity has not been optimal among them. In this report, existing architectures are reviewed with some numerical evaluation. Our proposed architecture, modi_ed decoding parameter propagation (MDPP), is based on pixel domain transcoding with 4 supported modes. It takes the advantages on high visual performance and no latency is introduced. In the proposed architecture, incoming information is thoroughly reused for minimum computation complexity. Performance is enhanced by two-level search to avoid any mode mismatch while 7 search iterations are removed. Extensive experimental results shows that 99% of complexity is marvelously reduced compared with the cascaded pixel domain transcoder. Besides, 5~8 speedup is achieved by MDPP over the multi-mode architectures. Referring to the video quality, our architecture reaches high performance among the conventional techniques. The proposed architecture is believed to be the optimal choice between performance and complexity.
