Efficient Video Transcoding from H.263 to H.264/AVC Standard with Enhanced Rate Control
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Efficient Video Transcoding from H.263 to H.264/AVC Standard with Enhanced Rate Control Viet-Anh Nguyen and Yap-Peng Tan School of Electrical & Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798 Received 11 August 2005; Revised 25 December 2005; Accepted 18 February 2006 A new video coding standard H.264/AVC has been recently developed and standardized. The standard represents a number of advances in video coding technology in terms of both coding efficiency and flexibility and is expected to replace the existing standards such as H.263 and MPEG-1/2/4 in many possible applications. In this paper we investigate and present efficient syntax transcoding and downsizing transcoding methods from H.263 to H.264/AVC standard. Specifically, we propose an efficient motion vector reestimation scheme using vector median filtering and a fast intraprediction mode selection scheme based on coarse edge information obtained from integer-transform coefficients. Furthermore, an enhanced rate control method based on a quadratic model is proposed for selecting quantization parameters at the sequence and frame levels together with a new frame-layer bit allocation scheme based on the side information in the precoded video. Extensive experiments have been conducted and the results show the efficiency and effectiveness of the proposed methods. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
The presence of various efficient video coding standards has resulted in a large number of videos produced and stored in different compressed forms [1]. These coding standards compress videos to meet closely the constraints of their target applications, such as available transmission bandwidth, desired spatial or temporal resolution, error resilience, and so forth. Consequently, videos compressed for one application may not be well suited for other applications subject to a set of more restricted constraints, for example, a lower channel capacity or a smaller display screen. To a certain extent, this mismatch in application constraints has hindered efficient sharing of compressed videos among today’s heterogeneous networks and devices. To address such inefficiency, video transcoding has been proposed to convert an existing compressed video to a new compressed video in a different format or syntax [2, 3]. Video transcoding techniques can be broadly classified into homogenous and heterogenous transcodings. Homogeneous transcoding is generally used to reduce the bitrate, frame rate, and/or spatial resolution (downsizing transcoding) so that the processed video can suit better the new application constraints (e.g., small display screen, limited processing resource, or scarce transmission capacity). On the other
hand, heterogenous transcoding is used to change the syntax of a compressed video (syntax transcoding) for decoders compliant to a different compression standard, such as the conversion between MPEG-2 and H.263 standards [4]. To meet the requirements of many potential real-time applicatio
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