Unbalanced Quantized Multiple State Video Coding
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Unbalanced Quantized Multiple State Video Coding Sila Ekmekci Flierl,1 Thomas Sikora,2 and Pascal Frossard1 1 Ecole ´
Polytechnique F´ed´erale de Lausanne (EPFL), Signal Processing Institute, 1015 Lausanne, Switzerland for Telecommunications, Technical University Berlin, 10587 Berlin, Germany
2 Institute
Received 18 March 2005; Revised 24 August 2005; Accepted 12 September 2005 Multiple state video coding (MSVC) is a multiple description scheme based on frame-wise splitting of the video sequence into two or more subsequences. Each subsequence is encoded separately to generate descriptions which can be decoded independently. Due to subsequence splitting, the prediction gain decreases. But since reconstruction capabilities improve, error resilience of the system increases. Our focus is on multiple state video coding with unbalanced quantized descriptions, which is particularly interesting for video streaming applications over heterogeneous networks where path diversity is used and transmission channels have varying transmission characteristics. The total bitrate is kept constant, while the subsequences are quantized with different stepsizes depending on the sequence as well as on the transmission conditions. Our goal is to figure out under which transmission conditions unbalanced bitstreams lead to good system performance in terms of the average reconstructed PSNR. Besides, we investigate the effects of intra-coding on the error resilience of the system and show that the sequence characteristics, and in particular the degree of motion in the sequence, have an important impact on the decoding performance. Finally, we propose a distortion model that is the core of an optimized rate allocation strategy, which is dependent on the network characteristics and status as well as on the video sequence characteristics. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
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INTRODUCTION
Multimedia communication over the Internet has conflicting requirements on high compression and high error resilience. Multiple description coding (MDC) is an error resilient source coding method, where two or more descriptions of the source are sent to the receiver over different channels. If only one description i is received, the signal is reconstructed with distortion Di . If all descriptions are available, we achieve a lower distortion D0 . Multiple state video coding (MSVC) is a special multiple description scheme where the video sequence is splitted into the subsequences of even and odd numbered frames [1]. An MSVC system has two main components: multiple state encoding/decoding and a path diversity transmission system. The generated subsequences are coded into multiple independently decodable streams each with its own prediction process and state. The advantages are that the streams are decodable independently and that the correctly received stream can enable state recovery for the corrupted stream using bidirectional information from past and future frames. With the increasing heterogeneity in network infrastructures,
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