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 right 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 [1] 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 design and apply four saliency reduction operators iteratively in a loop, in order to reduce the saliency of candidate blocks. Experimental results show that: i) PSNR of the error-concealed frames can be increased dramatically (up to 3.2dB over the original RE-CAP), showing the effectiveness of a low-saliency prior in the underdetermined error concealment problem; and ii) subjective quality of the repaired video using our proposal, as confirmed by an extensive user study, is better than the original RECAP.Index Terms-Video streaming, error concealment, visual saliency
INTRODUCTIONDespite ongoing efforts to further advance communication technologies, high quality real-time video streaming over best-effort, packetswitched networks remains challenging for a number of reasons. First, consumer demand for interactive streaming video (e.g., conference video such as Skype, Google Talk, etc.) continues to outpace the rate of increase in network bandwidth [2], resulting in congestion and packet queue overflows in packet-switched networks. Second, when packet losses do occur, persistent server-client retransmission is not practical due to the timing constraint of streaming video (i.e., a video packet arriving at decoder past its playback deadline is useless). Third, new media types such as ultra-high-resolution videoThis work was supported in part by the NSERC grant RGPIN 327249.and multiple-view video [3] that promise enhancement of viewing experience are also further straini...