Effect of concealment techniques on perceived video quality

We study the effects of channel losses on block-based coders over packet-switched networks. Such coders rely on motion-compensated block prediction with intra refresh and/or intra-coded conditional replenishment for robust data compression. We consider a motion-compensated prediction coder that optimizes the coding mode selection (inter/intra) based on channel loss characteristics. We also consider an intra-frame coder with conditional replenishment. We assume that a packet contains a single block and the associated prediction parameters and that rnacroblock losses are independent. We investigate various error concealment strategies and evaluate their effects on perceived video quality. One approach is to use spatial interpolation techniques to replace the lost packets. An alternative approach is to use (appropriately shifted) temporal replacement. In the case of motion-compensated prediction, the motion vectors of neighboring blocks are used to obtain an approximation of the lost block from the previous frame. For the intra-frame coder with conditional replenishment, a lost packet is replaced by the block at the same location in the previous frame. Our results indicate that temporal replacement results in lower perceptual distortion than spatial interpolation. We also found that, when the packet containing the residual error is received but the motion-compensated prediction depends on blocks that have been lost, the lowest distortion results when the residual error is added only to the part of the signal that has not sustained any losses.