Content-Aware Scalability-Type Selection for Rate Adaptation of Scalable Video
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Research Article Content-Aware Scalability-Type Selection for Rate Adaptation of Scalable Video Emrah Akyol,1 A. Murat Tekalp,2 and M. Reha Civanlar3 1 Departmet
of Electrical Engineering, Henry Samuel School of Engineering and Applied Science, University of California, P.O. Box 951594, Los Angeles, CA 90095-1594, USA 2 Department of Electrical and Computer Engineering, College of Engineering, Koc ¸ University, 34450 Sariyer, Istanbul, Turkey 3 DoCoMo USA Labs, Palo Alto, CA 94304-1201, USA Received 4 October 2006; Revised 31 December 2006; Accepted 14 February 2007 Recommended by Chia-Wen Lin Scalable video coders provide different scaling options, such as temporal, spatial, and SNR scalabilities, where rate reduction by discarding enhancement layers of different scalability-type results in different kinds and/or levels of visual distortion depend on the content and bitrate. This dependency between scalability type, video content, and bitrate is not well investigated in the literature. To this effect, we first propose an objective function that quantifies flatness, blockiness, blurriness, and temporal jerkiness artifacts caused by rate reduction by spatial size, frame rate, and quantization parameter scaling. Next, the weights of this objective function are determined for different content (shot) types and different bitrates using a training procedure with subjective evaluation. Finally, a method is proposed for choosing the best scaling type for each temporal segment that results in minimum visual distortion according to this objective function given the content type of temporal segments. Two subjective tests have been performed to validate the proposed procedure for content-aware selection of the best scalability type on soccer videos. Soccer videos scaled from 600 kbps to 100 kbps by the proposed content-aware selection of scalability type have been found visually superior to those that are scaled using a single scalability option over the whole sequence. Copyright © 2007 Emrah Akyol et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Scalable video coding has gained renewed interest since it has been shown [1, 2] that it can achieve compression efficiency that is close to that of H.264/AVC [3] while providing a flexible adaptation to time-varying network conditions and heterogeneous receiver capabilities. Scalable video coding methods can be clustered into two groups according to the spatial transforms they utilize, block-based and wavelet-based coders. All scalable video coders enable postencoding flexible adaptation of video rate through signal-tonoise ratio (SNR), temporal, and/or spatial scalability [1, 2]. They employ motion-compensated temporal filtering (flexible temporal predictions, such as hierarchical B pictures in block-based scalable coders and open-loop MCTF in wavelet coders) to provide temporal scalability, follow
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