Efficient and Reliable Video Streaming based on Frame Dependency Design

基於畫面相依性的高效率與高可靠度視訊串流設計

楊凱超(Kai-Chao Yang)

指導教授 ： 王家祥

國立清華大學/電機資訊學院/資訊工程學系/博士(2009年)

https://doi.org/10.6843/NTHU.2009.00138

摘要

在視訊串流服務中，使用者向伺服器端要求不同的影片播放，而伺服器則利用Chaining或Broadcasting等各種串流技術將影片傳送給使用者。對伺服器端而言，一般期望能減輕伺服器負擔與降低頻寬需求使其能服務更多的使用者。對使用者而言，提供完整提的VCR操作功能與穩定畫質則是主要需求。然而使用者的需求卻往往增加伺服器與骨幹網路的負擔。舉例來說，當使用者進行快轉或跳張等VCR動作時，傳送速度必須增加以趕上解碼端所要求的播放倍率。而播放倍率往往與所需的傳送速度成正比，如此便造成伺服器與網路的重大負擔。另一方面，當網路負擔加重時，封包丟失或延遲比例也隨之增加。當封包未及時送達時，解碼端必須選擇等待或放棄此封包，而造成畫面延遲或品質降低的後果。
我們在不嚴重降低編碼效率以及不增加網路負擔的前提下，探討如何利用視訊編碼技術滿足使用者的VCR要求以及正確補償丟失的封包。基於影像畫面之間的運動補償相依關係，我們利用改變畫面相依性來重新編碼影像，使其能有效率地支援VCR操作功能或是錯誤補償功能。利用我們所提出的編碼結構，能讓使用者在操作VCR功能時，幾乎不會增加網路以及伺服器的負擔，使得伺服器能同時服務的人數大量增加。此外，我們也發展出另一種編碼結構，使畫面因封包丟失或延遲造成損壞時，錯誤不會傳遞至相鄰的畫面。由於相鄰的前後兩張畫面仍能正確解壓縮，因此我們有更多的資訊可以回復錯誤的畫面，也讓使用者在觀看之時所受到的影響最低。
我們所提出的方法特別適用於低頻寬的網路環境下，例如手機與各種手持式裝置等。實驗證明，在儘量不增加網路頻寬的前提下，我們能有效率地支援VCR功能或是回復已發生的錯誤，同時也減經伺服器的負擔。

關鍵字

視訊串流 ； VCR ； 容錯編碼 ； GOP ； H.264/AVC

並列摘要

In a video streaming system, the server sends requested videos to end users by unicasting, broadcasting, chaining, or other streaming techniques. Intuitively, the goal of the server is reduction of server load and bandwidth requirements to serve more users. For client sides, a smooth quality, low delay time, and full VCR functionality might be the most important requirements. However, it is trade-off to fulfill both the user requirements and the server goal because these user requirements usually cause serious server and network load. For example, the server has to send a stream with triple transmission rate than usual when a fast scan operation at speed factor three is requested. According to our simulation, the transmission rate is normally proportional to the requested speed factor. When the network load becomes heavy, there will be more serious packet loss, leading to delay or unstable quality.
In the thesis, several novel video coding structures are proposed to support VCR functionalities and error resilience with little loss of coding efficiency. Based on the temporal dependency between frames in a GOP, we reconstruct the coding dependency in the GOP to support effective access of frames and stop error propagation. With one of the proposed structures, the server does not have to speed up the transmission rate of frames to fulfill the requested playback rate. The number of frames to be transmitted is also significantly reduced, and thus the network load can be decreased. With the other proposed structure, error propagation can be significantly reduce, and errors in one frame will not propagate to neighboring frames, such that the damaged frame can be recovered from its neighbors.

並列關鍵字

Video streaming ； VCR ； Error resilience ； GOP ； H.264/AVC

參考文獻

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