Video Error Concealment Using a Computation-Efficient Low Saliency Prior

Error concealment in packet-loss-corrupted streaming video is inherently an under-determined problem, as there are insufficient number of well-defined criteria to recover the missing blocks perfectly. When a Region-of-Interest (ROI) based unequal error protection (UEP) scheme is deployed during video streaming-i.e., more visually salient regions are strongly protected-a lost block is likely to be of low saliency in the original frame. In this paper, we propose to add a low-saliency prior to the error concealment problem as a regularization term. It serves two purposes. First, in ROI-based UEP video streaming, low-saliency prior provides the correct side information for the client to identify the correct replacement blocks for concealment. Second, in the event that a perfectly matched block cannot be unambiguously identified, the low-saliency prior reduces viewer´s visual attention on the loss-stricken region, resulting in higher overall subjective quality. We study the effectiveness of a low-saliency prior in the context of a previously proposed RECAP error concealment system. RECAP transmits a low-resolution (LR) version of an image alongside the original high-resolution (HR) version, so that if blocks in the HR version are lost, the correctly-received LR version can serve as a template for matching of suitable replacement blocks from a previously correctly-decoded HR frame. We add a low-saliency prior to the block identification process, so that only replacement candidate blocks with good match and low saliency can be selected. Further, we develop a low-complexity convex approximation to the well known Itti-Koch-Niebur saliency model, which enables the low-saliency error concealment problem to be solved efficiently. Experimental results show that: i) PSNR of the error-concealed frames can be increased dramatically (up to 3.6 dB over the original RECAP), showing the effectiveness of a low-saliency prior in the under-determined error concealment problem; and ii) s- bjective quality of the repaired video using our proposal, as confirmed by an extensive user study, is better than the original RECAP.