不同網路環境下的傳輸頻寬能力皆不相同，伺服端透過有線或無線網路以即時的方式傳輸視訊串流至電腦或手機…等用戶端時，如何使視訊串流滿足各種頻寬要求是一大課題，本篇論文以轉換編碼(transcoding)的方式將原以較高位元率及高解度壓縮之H.264 視訊串流轉換編碼成為較低位元率及低解析度壓縮的H.264 視訊串流，使其能適應當下的網路頻寬要求並有效的利用頻寬，進而讓用戶端可順暢的播放視訊影片並獲得較佳的畫面品質。而在H.264 中加入很多了高複雜度的預測和壓縮技術，使其可以提供比以往的視訊壓縮標準更佳的壓縮效能，但同時也因此讓H.264 編碼端複雜度過高，若要將之運用於即時之轉換編碼系統是有難度的，本篇論文即是針對H.264 轉換編碼，探討如何在降低位元速率及解析度之應用下以最快的速度進行轉換編碼，並提出了快速畫面間預測轉換編碼演算法，實驗結果顯示本篇論文所提出之兩種轉換編碼演算法，能在維持一定的畫面品質效能下，有效的加速轉換編碼時間。 Through wired or wireless network, the server transmits real-time video bit-stream to the client device, such as computer and cellular phone. To efficiently transmit video bit-stream form high resolution to low resolution would be difficult since the bandwidth varies in different network environment. In this thesis, we will increase the compression ratio of the H.264 transcoder to reduce bit-rate and change video resolution stream, thence to achieve efficiency in video bit-stream transmission and improve bandwidth utilization for different devices. In this way, the client can play video smoothly and get a better image quality. H.264 supports many advanced compression techniques that can achieve better coding performance than the previous standards. However, the compression techniques require high computational complexity, which would be difficult to achieve real time implementation. In this thesis, we will explore how to perform H.264 bit-rate reduction and down-resolution transcoding as fast as possible and propose fast intra and inter frame prediction transcoding algorithms. The experimental results show that our propose transcoding algorithms can maintain the coding performance and speed up transcoding process simultaneously.
