Unbalanced Multiple-Description Video Coding with Rate-Distortion Optimization
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Unbalanced Multiple-Description Video Coding with Rate-Distortion Optimization David Comas Image Processing Group, Department of Signal Theory and Communications, Technical University of Catalonia (UPC), 08034 Barcelona, Spain Email: [email protected]
Raghavendra Singh IBM India Research Lab., Indian Institute of Technology (IIT) Delhi, New Delhi, India Email: [email protected]
Antonio Ortega Signal and Image Processing Institute and Integrated Media Systems Center, Department of Electrical Engineering, University of Southern California, Los Angeles, CA 90089-2564, USA Email: [email protected]
´ Ferran Marques Image Processing Group, Department of Signal Theory and Communications, Technical University of Catalonia (UPC), 08034 Barcelona, Spain Email: [email protected] Received 7 May 2002 and in revised form 11 November 2002 We propose to use multiple-description coding (MDC) to protect video information against packet losses and delay, while also ensuring that it can be decoded using a standard decoder. Video data are encoded into a high-resolution stream using a standard compliant encoder. In addition, a low-resolution stream is generated by duplicating the relevant information (motion vectors, headers and some of the DCT coefficient) from the high-resolution stream while the remaining coefficients are set to zero. Both streams are independently decodable by a standard decoder. However, only in case of losses in the high resolution description, the corresponding information from the low resolution stream is decoded, else the received high resolution description is decoded. The main contribution of this paper is an optimization algorithm which, given the loss ratio, allocates bits to both descriptions and selects the right number of coefficients to duplicate in the low-resolution stream so as to minimize the expected distortion at the decoder end. Keywords and phrases: multiple-description coding, robust video transmission, rate-distortion optimization, packet networks.
1.
INTRODUCTION
In recent years, the volume of multimedia data transmitted over best-effort networks such as the Internet has continued to increase while packet losses and delays, due to congestion, routing delay, and network heterogeneity, continue to be commonplace. In this paper, we address the issue of robust streaming of video data. Video data is usually encoded using predictive encoders, for example, motion compensation in the standard H.263 [1] and MPEG [2] encoders. These encoders take advantage of the temporal redundancy in the data to achieve high compression performance. However, the main drawback of a predictive coding scheme is that even
a single packet loss (or erasure) in the transmitted stream causes decoding errors to propagate through all the samples following the erasure. This severely affects the video quality available at the receiver and motivates the need for robust transmission of video data. A common approach to limit the length of error propagation in video coders is to restart the prediction loop by periodically in
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