Stephane Valente

An efficient error concealment implementation for MPEG-4 video streams

This paper presents an efficient error concealment implementation for damaged MPEG-4 video bitstreams. The chosen spatial and temporal concealment algorithms are designed to fit in real-time decoders and are advantageously combined in a hybrid spatial/temporal approach to provide visually more plausible pictures than basic concealment techniques. In addition, the encoder impact on the visual quality of the reconstruction in presence of channel errors is highlighted.

Rate/distortion-based combination of multiple DCT transforms for video coding

In this paper, we address the key problem in real-time video coding, the rate-distortion (R-D) tradeoff. As most video coding applications employ color images, we analyze the R-D modeling problem of the color image sequence. We investigate that the R-D characteristics of color video signal in traditional transform-based video coding systems should be modeled for the luminance and chrominance components separately. So we propose separable R-D models for color video coding. The feedback from the encoder buffer is analyzed by a control-theoretic adaptation approach to avoid buffer overflow and underflow. To achieve smooth video quality and satisfy the delay constraints in real-time applications, a novel R-D tradeoff controller is designed. In the proposed R-D tradeoff framework, both the quality variation and buffer safety are considered. Extensive simulation results demonstrate that the proposed approach can achieve smooth video quality without sacrificing overall quality while efficiently utilize the bandwidth without buffer overflow or underflowThis paper proposes some early results concerning the combination of discrete cosine transforms (DCTs) of multiple sizes in a video encoder. The main difficulty consists in finding a way to obtain a fair competition between several transforms. For that purpose, we derive that the quantization of all transformed coefficients regardless of the DCT size with the same uniform linear quantizer allows to obtain an equivalent level of distortion among all transforms. The selection of the best transform on a particular image area is then made by a rate/distortion framework, which jointly optimizes motion and residual signal coding. Systematic objective and subjective improvements are observed when compared to using a single DCT size.