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Proceedings Paper

Perceptual vector quantization for video coding
Author(s): Jean-Marc Valin; Timothy B. Terriberry
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Paper Abstract

This paper applies energy conservation principles to the Daala video codec using gain-shape vector quantization to encode a vector of AC coefficients as a length (gain) and direction (shape). The technique originates from the CELT mode of the Opus audio codec, where it is used to conserve the spectral envelope of an audio signal. Conserving energy in video has the potential to preserve textures rather than low-passing them. Explicitly quantizing a gain allows a simple contrast masking model with no signaling cost. Vector quantizing the shape keeps the number of degrees of freedom the same as scalar quantization, avoiding redundancy in the representation. We demonstrate how to predict the vector by transforming the space it is encoded in, rather than subtracting off the predictor, which would make energy conservation impossible. We also derive an encoding of the vector-quantized codewords that takes advantage of their non-uniform distribution. We show that the resulting technique outperforms scalar quantization by an average of 0.90 dB on still images, equivalent to a 24.8% reduction in bitrate at equal quality, while for videos, the improvement averages 0.83 dB, equivalent to a 13.7% reduction in bitrate.

Paper Details

Date Published: 4 March 2015
PDF: 11 pages
Proc. SPIE 9410, Visual Information Processing and Communication VI, 941009 (4 March 2015); doi: 10.1117/12.2080529
Show Author Affiliations
Jean-Marc Valin, Mozilla (United States)
Timothy B. Terriberry, Mozilla (United States)
Xiph. Org Foundation (United States)

Published in SPIE Proceedings Vol. 9410:
Visual Information Processing and Communication VI
Amir Said; Onur G. Guleryuz; Robert L. Stevenson, Editor(s)

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