發(fā)布時間：2018-12-29 07:27

【摘要】：基于HTTP的動態(tài)自適應(yīng)流媒體技術(shù),主要是根據(jù)網(wǎng)絡(luò)狀況以及設(shè)備性能動態(tài)調(diào)整播放媒體文件的碼率,實現(xiàn)多媒體內(nèi)容的無縫傳送和播放。碼率自適應(yīng)算法作為動態(tài)自適應(yīng)流媒體技術(shù)的關(guān)鍵,一直是學術(shù)界的一個研究熱點。通過對現(xiàn)有碼率自適應(yīng)算法進行分析后發(fā)現(xiàn):(1)基于帶寬的碼率自適應(yīng)算法在播放開始時會長時間選擇碼率較低的切片進行下載,導(dǎo)致帶寬利用率較低;(2)基于緩存的碼率自適應(yīng)算法對帶寬變化比較敏感,容易造成頻繁和大幅度的碼率切換,嚴重影響用戶體驗質(zhì)量;(3)基于緩沖區(qū)等級的碼率自適應(yīng)算法,在播放開始階段的切片碼率提升較慢,并且在帶寬波動較大的環(huán)境下,客戶端緩沖區(qū)變化幅度較大。鑒于目前的算法存在上述問題,對碼率自適應(yīng)算法的研究也顯得至關(guān)重要。本文首先研究了基于HTTP的自適應(yīng)流媒體技術(shù)的主要特點,并對現(xiàn)有自適應(yīng)流媒體技術(shù)的企業(yè)方案進行了介紹和分析。其次,本文重點研究了旨在為動態(tài)自適應(yīng)流媒體技術(shù)提供統(tǒng)一標準的MPEG-DASH及其相關(guān)技術(shù)。然后,本文對現(xiàn)有碼率自適應(yīng)算法進行了研究和分析,并針對算法目前存在的問題,提出了一種基于緩沖區(qū)等級的改進算法。該算法在保證緩沖區(qū)狀態(tài)穩(wěn)定的條件下,減少了碼率切換次數(shù),提升了播放開始階段的切片碼率。同時,本文依據(jù)自適應(yīng)播放過程中影響用戶體驗質(zhì)量(Quality of Experience,Qo E)的主要因素,定義了Qo E評價指標和評價函數(shù),并利用層次分析法確定了評價函數(shù)中不同指標的權(quán)重系數(shù),最終實現(xiàn)了對自適應(yīng)算法的客觀評價。最后,本文在基于Android的客戶端中實現(xiàn)了提出的改進算法以及對比算法,并利用Web服務(wù)器和網(wǎng)絡(luò)模擬工具對算法在不同網(wǎng)絡(luò)環(huán)境中的性能表現(xiàn)進行了實驗驗證和QoE分析。實驗結(jié)果表明,本文提出的改進算法在受限的不變網(wǎng)絡(luò)環(huán)境和連續(xù)波動的網(wǎng)絡(luò)環(huán)境中表現(xiàn)相對穩(wěn)定。在保證緩沖區(qū)穩(wěn)定的前提下,提出的改進算法在帶寬呈現(xiàn)階梯狀變化的網(wǎng)絡(luò)環(huán)境下同樣有著良好的性能表現(xiàn)。同時,通過利用Qo E評價函數(shù)對不同算法在連續(xù)波動網(wǎng)絡(luò)環(huán)境和帶寬階梯狀網(wǎng)絡(luò)環(huán)境下的QoE值進行計算后發(fā)現(xiàn),提出的改進算法在波動網(wǎng)絡(luò)環(huán)境下能夠提升用戶的體驗質(zhì)量。
[Abstract]:The dynamic adaptive streaming media technology based on HTTP mainly adjusts the code rate of playing media files dynamically according to the network condition and equipment performance to realize the seamless transmission and playback of multimedia content. As a key technology of dynamic adaptive streaming media, rate adaptive algorithm has been a hot research topic in academia. Through the analysis of the existing rate adaptive algorithm, we find that: (1) the bandwidth based rate adaptive algorithm will select the lower bit rate slice to download at the beginning of playback, which leads to low bandwidth utilization; (2) the rate adaptive algorithm based on cache is sensitive to bandwidth change, and it is easy to cause frequent and large rate switching, which seriously affects the quality of user experience. (3) the bit-rate adaptive algorithm based on buffer level increases the bit rate slowly at the beginning stage of playback, and the client-side buffer varies greatly in the environment of high bandwidth fluctuation. In view of the above problems in the current algorithm, it is very important to study the rate adaptive algorithm. In this paper, the main characteristics of adaptive streaming media technology based on HTTP are studied, and the enterprise solutions of the existing adaptive streaming media technology are introduced and analyzed. Secondly, this paper focuses on MPEG-DASH and its related technologies, which aim to provide uniform standard for dynamic adaptive streaming media technology. Then, the existing rate adaptive algorithm is studied and analyzed, and an improved algorithm based on buffer level is proposed to solve the existing problems of the algorithm. Under the condition that the buffer state is stable, the algorithm reduces the number of bit rate switching and improves the slice rate at the beginning stage of playback. At the same time, according to the main factors that affect the user experience quality (Quality of Experience,Qo E) in the process of adaptive playback, the evaluation index and function of Qo E are defined. The weight coefficients of different indexes in the evaluation function are determined by using the analytic hierarchy process (AHP), and the objective evaluation of the adaptive algorithm is finally realized. Finally, the improved algorithm and the contrast algorithm are implemented in the client based on Android, and the performance of the algorithm in different network environment is verified and analyzed by using Web server and network simulation tools. The experimental results show that the proposed improved algorithm is relatively stable in the restricted invariant network environment and the continuous fluctuating network environment. On the premise of ensuring buffer stability, the proposed improved algorithm also has a good performance in the network environment where the bandwidth of the network presents ladder changes. At the same time, by using the Qo E evaluation function to calculate the QoE values of different algorithms in the continuous fluctuating network environment and the bandwidth ladder network environment, it is found that the improved algorithm can improve the user's experience quality in the fluctuating network environment.
【學位授予單位】：廣東工業(yè)大學
【學位級別】：碩士
【學位授予年份】：2017
【分類號】：TN919.8

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本文編號：2394491