| 摘要: | 隨選視訊（Video on Demand，VoD）是由使用者透過網路來觀看想看的影片的一種服務。由於網路科技的進步以及電腦速度及儲存體能力的不斷成長，提供隨選視訊的服務將變成有可能的一件事。 為了降低頻寬與磁碟傳輸的負擔，於是就有學者提出一種稱為熱門影片廣播法的播送方式，因為伺服器播送影片所用的頻寬跟使用者人數無關，所以這個方法適合用於播送多人收看的熱門影片。過去的方法都是假設切割的影片是固定位元率（Constant Bit Rate，CBR）編碼的影片，所以無法支援變動位元率（Variable Bit Rate，VBR）編碼的影片。根據研究，在相同品質畫面編碼的影片，CBR的平均位元率比VBR的平均位元率多兩倍以上，所以採取VBR編碼可能可以改善系統效能。 在本論文中，我們提出了兩個支援VBR影片的熱門影片廣播法，分別為整數切割（SFB）與非正數切割（SVHB）的方法。我們提出的方法減緩了頻寬的起伏，並且保證播放的連續性，其中SVHB是所需要資源最低的播送法，而SFB是一個可提供有起伏上限的播送法。 One way to broadcast a popular video is to partition the video into segments, which are broadcasted on several streams periodically. The approach lets multiple users share streams; thus, the stress on the scarce bandwidth can be alleviated without sacrificing viewers’ waiting time. One representative approach is the Harmonic Broadcasting (HB) scheme, which can broadcast a video using multiple streams by having new viewers wait no longer than L/N time, where L is the length of a video, and N is the number of segments. In comparison with other segmented schemes, the HB scheme requires minimum bandwidth. Another representative approach is the Fast Broadcasting (FB) scheme, which can broadcast a video using multiple streams by having new viewers wait no longer than L/N time, where L is the length of a video, and K is the number of streams. However, the schemes mainly support transmission of CBR-encoded videos. In this paper, we propose a simple VBR harmonic broadcasting (SVHB) scheme and a FB-based scheme for VBR-encoded videos. The first scheme, unlike the HB scheme, guarantees continuous playout. Additionally, SVHB improves the variable bandwidth harmonic broadcasting (VBHB) scheme in bandwidth consumption, maximum buffer requirements, and maximum required disk transfer rate. The second scheme can smooth required bandwidth. For a video, the maximum difference of its required bandwidth is less or equal to max(Bi - bi) , where Bi and bi represent the maximum and minimum required bandwidth on stream i,i = [1,N]. Some bounds on the bandwidth consumption, the buffer requirements, and the required disk transfer rate are also developed. |
