No abstract

Detection and localization of actions in videos is an important problem in practice. A traffic analyst might be interested in studying the patterns in which vehicles move at a given intersection. State-of-the-art video analytics systems are unable to efficiently and effectively answer such action queries. The reasons are threefold. First, action detection and localization tasks require computationally expensive deep neural networks. Second, actions are often rare events. Third, actions are spread across a sequence of frames. It is important to take the entire sequence of frames into context for effectively answering the query. It is critical to quickly skim through the irrelevant parts of the video to answer the action query efficiently.In this paper, we present Zeus, a video analytics system tailored for answering action queries. We propose a novel technique for efficiently answering these queries using a deep reinforcement learning agent. Zeus trains an agent that learns to adaptively modify the input video segments to an action classification network. The agent alters the input segments along three dimensions -sampling rate, segment length, and resolution. Besides efficiency, Zeus is capable of answering the query at a user-specified target accuracy using a query optimizer that trains the agent based on an accuracy-aware reward function. Our evaluation of Zeus on a novel action localization dataset shows that it outperforms the state-of-the-art frameand window-based techniques by up to 1.4× and 3×, respectively. Furthermore, unlike the frame-based technique, it satisfies the userspecified target accuracy across all the queries, at up to 2× higher accuracy, than frame-based methods.

State-of-the-art video database management systems (VDBMSs) often use lightweight proxy models to accelerate object retrieval and aggregate queries. The key assumption underlying these systems is that the proxy model is an order of magnitude faster than the heavyweight oracle model. However, recent advances in computer vision have invalidated this assumption. Inference time of recently proposed oracle models is on par with or even lower than the proxy models used in state-of-the-art (SoTA) VDBMSs. This paper presents Seiden, a VDBMS that leverages this radical shift in the runtime gap between the oracle and proxy models. Instead of relying on a proxy model, Seiden directly applies the oracle model over a subset of frames to build a query-agnostic index, and samples additional frames to answer the query using an exploration-exploitation scheme during query processing. By leveraging the temporal continuity of the video and the output of the oracle model on the sampled frames, Seiden delivers faster query processing and better query accuracy than SoTA VDBMSs. Our empirical evaluation shows that Seiden is on average 6.6 x faster than SoTA VDBMSs across diverse queries and datasets.