多媒體應用之影像平順播放器

Abstract

多媒體系統把許多不同的媒體(如文字、聲音、圖形和影像)資訊合併在一 起。為了滿足多媒體系統的需求有許多機制是必備的。尤其當資料經網路 傳輸時，每一封包(packet) 的傳輸延遲時間不同，此將嚴重影響影像、 聲音在遠端播放的效果。本論文首先對影像平順播放的問題做一深入的剖 析。其次，針對現有影像遠端播放演算法的缺點，提出一個能對網路傳輸 延遲的不定性做出即時回應的演算法，稱之為影像平順播放器(Video Smoother)。根據此演算法推導出一數學模型，並加以分析。再者，本論 文提出一個影像視訊會議系統(Video Teleconferencing System)的雛型 ，其將影像平順播放器置於傳輸層(Transport Layer)中，使得應用層( Application Layer)能不受網路狀態影響，達到影像平順播放的目的。最 後，我們將呈現此影像平順播放器之顯著成效。 Multimedia applications combine a variety of information, such as text,audio,graph,images,and video.To support multimedia applications,several facilities have been recongnized as assential.In particular,synchronization of single medium is significant of solving the discontinuity problem occurring when accessing remote media data.The thesis initially gives an in- depth survey of existing single medium synchronization mechanisms,especially the video/audio playout smoothing mechanisms.Although many mechanisms have been proposed,a general solution has not been indentified. The thesis then proposes a general and adaptive playout smoothing algorithm, called the Video Smoother,for solving the discontinuity problem. The Video Smoother adopts state- dependent playout rate;that is, the mean playout rate depends on the number of frames in the buffer.Since the state of the buffer reflects the state of the path through which the video frames are retrieved,the Video Smoother allows video playout to be dynamically adaptable to various network dealys.Suitable strategies for adapting playout rate under different loads are recommended according to analytic results. Moreover,a teleconferencing prototyping system with the Video Smoother employed as a part of the transport layer logic is developed to examine the performance of the Video Smoother.Prototyping results show the feasibility of the Video Smoother for the discontinuity problem.