應用於雜訊網路通道具容錯能力的可調式視訊傳輸之研究

Abstract

近年來因為寬頻服務的日趨成熟，多媒體串流技術和點對點(P2P)分散式網路架構的隨選視訊點播服務的傳輸與流通量也越來越大，在現有的網路傳輸系統中，存在封包遺失累積問題，因此穩定可靠的多媒體數據傳輸方法正成為越來越重要的研究主題。其中，在典型的多媒體通信應用中高效率容錯和錯誤恢復能力的演算法透過分析和數值方法來實現多目標優化性能指標的有效技術。與傳統數據通信的特點相較，多媒體串流有四個方面的主要差別: (1)、封包丟失是視訊串流品質不確定性的主要原因之一，並可能會導致許多有價值的視訊資訊缺失，進而造成影像品質嚴重下降。(2)、總頻寬的需求仍遠遠超過了現有的通信網絡基礎設施(如：支援高品質視訊隨選點播服務)。(3)、雖然在客戶端的緩衝器設計可以吸收傳輸速率的變化，但這不足以保證多媒體串流的服務品質(如：網路電視和網路電話）。(4)、雖然大多數的多媒體數據壓縮傳送允許應用在漏失封包和多錯誤的網路環境，並且由於人類視覺感知系統對於某些影像的變化不夠敏感，因此能容忍有某些程度的影像品質下降。進而，在視頻傳輸可調式編碼的基礎上使用錯誤控制和非均等錯誤保護碼可以是一個廣為被接受的方法來改善接收到的視訊品質。 在本論文中我們針對視訊串流在不斷變化的網路條件中，提出可擴展性、具錯誤容忍度和有效的錯誤保護的演算法，來達成系統優化性能之有效視訊傳輸技術。我們針對在漏失封包和多錯誤的網路環境下提出一個三維小波可調式視訊編碼演算法為基礎的內容自適應之錯誤保護技術，利用細緻可調式的方式去增強資料錯誤的保護能力。所提出的細緻可調式之錯誤保護演算法可在視訊編碼率和影像失真之間選擇一個適當的折衷，以適切決定可調式視訊編碼率和通道編碼-前向錯誤更正碼的保護安排。實驗結果顯示，確實能達成在多媒體數據傳輸應用中重建視訊品質和系統容錯能力之間的平衡。在P2P分散式網路架構的視訊串流之研究中，我們結合非結構性對等網路運算與隨選視訊技術，發展一套以視訊編碼之失真模型為基礎的複本容錯機制，希望藉由有效的佈建高視訊品質影響及高點播率之複本於點播視訊流中高失真區與非連續區域來提升整體服務成效。根據模擬實驗證明我們所提的方法，相對於其它的容錯機制，在點對點網路環境中廣泛存在的搭便車 (free-rider) 現象出現時亦可有效的降低終端使用者間影像品質損失，並在不同點對點網路條件下能有較穩定的視訊撥放品質。整體而言本方法可以有效降低隨選視訊服務伺服器的工作負載。

Due to the growing maturity of broadband services, multimedia streaming systems and peer-to-peer on demand service are gaining vast popularity in recent times. Stable and reliable transmission of multimedia data is becoming increasingly important for multimedia communication over networks subject to packet erasures. To achieve stability and reliability, efficient fault-tolerant and error-resilience methods for multimedia communication are typical analytical and numerical approaches, so as to attain multi-objective performance metrics. The characteristics of video traffic differ substantially from those of traditional data traffic in four ways. First, packet loss is the major cause of nondeterministic distortion on the Internet and may have significant impact on perceptual quality of the streaming video. Second, aggregate bandwidth requirements, supporting video-on-demand services, are still far in excess of the existing communication network infrastructure. Third, although buffering on the client side can provide an opportunity to absorb variations in transmission rates, it is not sufficient to guarantee the service quality of multimedia streams like IPTV (Internet Protocol television) and VoIP (Voice over IP). Finally, most compressed media data are transmitted over lossy and error-prone networks, and a certain degree of quality degradation is tolerable due to noise in some regions which are below the threshold of human visual perception. Thus, video transmission based on scalable coding and unequal error protection codes can be one of the approaches of maintaining acceptable media quality in a network. Error control for video communication and resource allocation in peer-to-peer multimedia systems remain open issues and are the focus of this work. In this thesis, we built scalable, error-resilient, and high-performance multimedia frameworks to adapt to changing network conditions. We developed a framework of fine-level packetization schemes for the streaming of 3D wavelet-based video content over lossy packet networks. An adaptive fine-granularity unequal error protection algorithm was proposed to allow a tradeoff between rate and distortion, and jointly adopt scalable source coding rates and the level of FEC protection. Experimental results show that the proposed framework strikes a fine balance between the reconstructed video quality and the level of error protection under time-varying lossy channels. In the study of P2P video streaming, we developed a replication strategy to optimize resource allocation based on the video-distortion technique for unstructured P2P overlay networks. Failure recovery action can be accomplished by distributing high quality impact and popular replicas to regions of low peers density or discontinuous areas. The results demonstrated the efficiency and robustness of the proposed method at compensating for network-induced errors, and the framework can be applied at a range of different scales of free-riding peers. Moreover, the proposed algorithm was able to handle the load imposed on the system efficiently and improved average visual quality in the overall system.