隨著網路通訊技術的進步，在網路上進行視訊傳輸已經變成非常熱門的應用。在傳統的多媒體傳輸系統上，通常會使用固定位元組率的編碼技術，因為用這種壓縮技術所壓縮的影片比較適合在網路上傳輸。但是，這種壓縮方式容易導致影片的畫面品質變得不穩定，進而影響使用者的滿意度。近年來，變動位元組率技術越來越受到重視，這是因為VBR壓縮的影片具有比較穩定的影像品質，但是，這種壓縮方式會導致影片的位元組率變化量甚大，使得這種影片不適合直接在網路上傳輸。
一個理想的視訊傳輸機制，應該能讓使用者觀看到影像品質平順的影片，而且要設法讓影片能順利地在網路上傳輸。因此，以變動位元組率的壓縮技術為主體，然後透過頻寬平順機制來抑制影片傳輸時的位元組率變化量，就成為一個可能的解決方案。然而，現有的頻寬平順機制的研究，多半都是建立在有保障服務品質的網路環境的假設之上，無法應用在盡力而為的網路環境。
因為目前的網路環境大部分都屬於盡力而為的網路，所以為此種網路來開發一套視訊傳輸機制是有必要性。在這篇論文中，我們提出一個視訊傳輸機制，來克服在盡力而為網路上傳輸影片的問題。這個傳輸機制提供擁塞控制機制，以避免造成網路的擁塞。此外，我們的機制也提供一套調整影像品質的機制，會依據網路可用的頻寬，適時去調整影像品質以符合網路可用頻寬的限制。在調整影像品質的同時，我們的機制也會盡可能設法讓影像品質能夠保持穩定。最後，憑藉以上的相關資訊，我們的傳輸機制會即時的計算出一個平順的傳輸排程，依據此排程，就能提供使用者一個品質穩定且有效率的多媒體播放服務。

With the rapid advances on network communications technologies, video streaming has become a very popular multimedia application on the network. In the traditional multimedia system, constant bit rate (CBR) compressed technique is usually used to encode video because the CBR videos are appropriate for transmission. But this compressed technique results in video quality becoming fluctuant. In recent years, the variable bit rate (VBR) compressed technique is becoming more and more importance. This is because that the VBR video can provide smooth quality video. But VBR compressed technique results in high rate variability of the video and makes the video not appropriate for transmission on the network directly.
An ideal video streaming mechanism should not only let user view smooth quality videos but also try to let videos transmit on the network smoothly. Therefore, we adopt VBR encoding technique to provide smooth quality videos to users and use bandwidth smoothing mechanism to reduce the bandwidth variation on transmitting these videos. However, majority of these researches for the bandwidth smoothing mechanism are based on the quality-of-service (QoS) network and can not be implemented on best-effort network.
In this thesis, we propose a video streaming mechanism on the best-effort network. Our streaming mechanism provides congestion control to prevent network from congestion. Moreover, our mechanism also provides quality adaptation mechanism to adapt the video quality according to the available bandwidth. While adapting the quality of a video, our scheme also attempts to smooth the perceptual quality for the user. Then, our scheme computes a smooth transmission schedule in real time. According to this smooth transmission schedule, we can provide a multimedia service with the stable quality and the high efficiency for user.

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