This paper addresses the problem of video coding in a joint source-channel setting. In particular, we propose a video encoding algorithm that prevents the indefinite propagation of errors in predictively encoded video-a problem that has received considerable attention over the last decade. This is accomplished by periodically transmitting a small amount of additional information, termed coset information, to the decoder, as opposed to the popular approach of periodic insertion of intra-coded frames. Perhaps surprisingly, the coset information is capable of correcting for errors, without the encoder having a precise knowledge of the lost packets that resulted in the errors. In the context of real-time transmission, the proposed approach entails a minimal loss in performance over conventional encoding in the absence of channel losses, while simultaneously allowing error recovery in the event of channel losses. We demonstrate the efficacy of the proposed approach through experimental evaluation. In particular, the performance of the proposed framework is 3-4 dB superior to the conventional approach of periodic insertion of intra-coded frames, and 1.5-2 dB away from an ideal system, with infinite decoding delay, operating at Shannon capacity.
Image-based rendering (IBR) and lightfield rendering (LFR) techniques aim to represent a 3D real-world environment by densely sampling it through a set of fixed viewpoint cameras. Remote digital walkthroughs of the 3D environment are facilitated by synthesizing novel viewpoints from the captured view-set. The large amount of data generated by the dense capture process makes the use of compression imperative for practical IBWLFR systems. In the present paper, we consider the design of compression techniques for streaming of IBR data to remote viewers. The key constraints that a compression algorithm for IBR streaming is required to satisfy, are those ofrandom access for interactivity, and precompression. We propose a compression algorithm based on the use of coset codes for this purpose. The proposed algorithm employs H.264 source compression in conjunction with LDPC coset codes to precompress the IBR data. Appropriate coset information is transmitted to the remote viewers to allow interactive view generation. Results indicate that the proposed compression algorithm provides good compression efficiency, while allowing client interactivity and server precompression.
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