Surveillance videos in smart environments have become commodities nowadays, which enable many novel applications, including various video analytics that turn videos into semantic results. In addition to live feeds, surveillance videos may be saved in a storage server for on-demand user-defined queries in the future. Different from on-demand video streaming servers, whose design objective is to maximize the user-perceived video quality, a surveillance video storage server has limited space and must retain as much information as possible while reserving sufficient space for incoming videos. In this article, we design, implement, optimize, and evaluate a multi-level feature driven storage server for diverse-scale smart environments, which can be buildings, campuses, communities, and cities. We focus on the design and implementation of the storage server and solve two key research problems in it, namely: (i) efficiently determining the information amount of incoming videos and (ii) intelligently deciding the qualities of videos to be kept. In particular, we first analyze the videos to derive approximate information amount without overloading our storage server. This is done by formally defining the information amount based on multi-level (semantic and visual) features of videos. We then leverage the information amounts to determine the optimal downsampling approach and target quality level of each video clip to save the storage space, while preserving as much information amount as possible. We rigorously formulate the above two research problems into mathematical optimization problems, and propose optimal, approximate, and efficient algorithms to solve them. Besides a suite of optimization algorithms, we also implement our proposed system on a smart campus testbed at NTHU, Taiwan, which consists of eight smart street lamps. The street lamps are equipped with a wide spectrum of sensors, network devices, analytics servers, and a storage server. We compare the performance of our proposed algorithms against the current practices using real surveillance videos from our smart campus testbed. Our efficient algorithms outperform the current practices in multiple dimensions, meaning we: (i) achieve a mere 7% approximation gap on captured information amount compared to the optimal solutions, (ii) save almost 3 times more clips after a week, (iii) achieve 58% less per-query error on average, (iv) always terminate in less than 100 ms, (v) do not consume excessive storage space, and (vi) scale well with larger storage spaces.
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Mar 28, 2024
Haiping Wang + 8
Open Access