現今多媒體編碼技術進步，加上網際網路的發達，多媒體通信的相關應用已成為人類日常生活中不可缺少的一項技術。例如微軟的Messenger (MSN)以及網路電話Skype等。因為Skype的視訊傳輸方法未公開，為了瞭解Skype及MSN在眾多使用者於網路上的服務品質，由於真正的媒體串流與使用者之接收品質難以直接量測，必須透過在傳送端與解碼端擷取聲音或影像，以評估上述兩種軟體的編碼與傳輸效能。另外一方面，由於公用網路上的流量難以精確的分離出封包來計算，因此本論文我們使用網路模擬器來限制傳送端傳輸通道的容量，以觀察通信軟體系統調適視訊編碼與傳輸的特性。本論文提出一量測網路電話視訊服務品質的系統，藉以瞭解其視訊編碼與傳輸的策略，作為設計相關視訊服務，例如P2P-IPTV的設計參考。我們利用虛擬攝影機(Virtual Camera) 與螢幕側錄程式來傳送與擷取影像，並利用網路損傷模擬器(Network Impairment Emulator)來控制網路環境的參數。藉由比較Skype及MSN在不同的網路環境參數下所提供的視訊之PSNR值，來推測其視訊編碼與傳輸的策略，以提供進一步設計相關網路多媒體系統的參考。

With the advance of multimedia codec design, together with the prevalence of network communications and utilizations, multimedia communication has become one of several technical applications for our everyday life. For example, MSN and Skype provide online voice and image communications and have become popular in recent years. Because the video codec of Skype, On2, was not officially released, and the behavior of real media packets is hard to measure, a network emulator was used to simulate the network environment parameters. For video quality evaluation, we proposed to records images from both encoder and decoder sides to evaluate the coding control performance of above two VOIP systems, from which the coding and transmission strategies can be utilized in IPTV related applications for better service quality, i.e., low delay and high frame rate et al. We compare the coding and transmission control performances of Skype and MSN under wired, e.g., Taiwan Academic Network, and wireless transmission environment, e.g., 3G and WLAN, which would help us to design robust multimedia communication systems with good quality service.

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