H.264可調式視訊編碼之品質可調編碼參數探討

H.264 可調式視訊編碼有空間可調性、時間可調性以及品質可調性，分別可以依照解析度、畫面張數以及PSNR等不同需求來調整畫面品質。相較於非可調式視訊編碼必須針對不同需求做不同的編碼，可調式視訊編碼只需要編碼一次就能夠對應不同的需求，可以大量節省編碼成本和傳輸的頻寬。本篇論文主要是分析H.264品質可調的編碼參數對於失真和複雜度的影響。H.264的品質可調有粗略可調(CGS)與中等可調(MGS)兩種方式，這兩種可調性可以單獨使用也可以一起使用。我們針對JSVM編碼軟體測試不同的參數配置，包括品質層的層數、量化參數、區塊大小等等，以各種不同CGS和MGS的混合層數來探討品質可調性編碼的效能。在研究的過程中，我們發現兩種可調性一起使用時有時候會有碼率失真表現異常的現象。經過實驗發現問題原因可能發生在層間預測的錯誤，我們因此提出一個方法，判定是否不使用較小的區塊來避免層間預測錯誤，而此方法也大幅縮減了編碼的時間。

關鍵字

可調式視訊編碼；品質可調性； H.264

並列摘要

Scalable video coding (SVC) encodes image sequences into a single bit stream that can be adapted to various network and terminal capabilities. The H.264/AVC standard includes three kinds of video scalability, namely spatial scalability, temporal scalability, and quality scalability. Among them, quality scalability refers to image sequences of the same spatio-temporal resolution but with different fidelity levels. Two options of quality scalability are adopted in H.264/AVC, CGS (coarse-grain quality scalable coding) and MGS (medium-grain quality scalability), and they may be used in combinations. In this thesis, we test various CGS/MGS options for H.264 SVC using the official reference software JSVM (Joint Scalable Video Model), such as the number of layers, quantization parameters, and block sizes. We combine CGS with MGS in order to achieve good rate-distortion and complexity performance. But the result is not always as expected for PSNR drops at some configurations. The anomaly may attribute to the inadequate　inter-layer prediction. We try to resolve the problem, by restricting　motion estimation with only larger matching blocks. The proposed method can also significantly reduce the encoding time.

並列關鍵字

Scalable Video Coding (SVC) ； Quality Scalability ； H.264

參考文獻

[1] Jens-Rainer Ohm, “Advances in scalable video coding,” Proceedings of the IEEE, vol. 93, no. 1, pp. 42-54, Jan. 2005.

[3] H. Schwarz, D. Marpe, and Thomas Wiegand, “Overview of the scalable video coding extension of the H.264/AVC standard,” IEEE Trans. Circuits Syst. Video Technol., vol. 17, no. 9, pp. 1103-1102, Sep. 2007.

[4] H. Schwarz and M. Wien, “The Scalable Video Coding Extension of the H.264/AVC Standard,” Standards in a nutshell, IEEE Signal Processing Magazine, vol. 25, no. 2, pp. 135-141, Mar. 2008.

[5] A. Pulipaka, P. Seeling, M. Reisslein, and L.J. Karam, “Overview and traffic characterization of coarse-grain quality scalable (CGS) H.264 SVC encoded video,” Consumer Communications and Networking Conference (CCNC), pp.1-5, Jan. 2010.

[6] B. Görkemli, Y. Şadi, and A.M. Tekalp, “Effects of MGS fragmentation, slice mode and extraction strategies on the performance of SVC with medium-grained scalability,” IEEE International Conference Image Processing (ICIP), pp.4201-4204, Sep. 2010.

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H.264可調式視訊編碼之品質可調編碼參數探討

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