The rapid proliferation of urban surveillance infrastructure and the exponential growth of large-scale video data have intensified demand for automated, adaptive monitoring solutions. Recent deep learning advances have transformed conventional surveillance from rule-based systems into adaptive, context-aware frameworks capable of complex spatiotemporal activity detection, classification, and interpretation. This paper presents a comprehensive review of seventy-three deep-learning-based research studies on video anomaly detection (VAD) and human activity recognition published between 2018 and 2025. A systematic categorization of the surveyed works is performed with respect to ten major model families: CNNs for spatial feature extraction recurrent architectures (LSTM, GRU, Bi-LSTM) for temporal reasoning; 3D-CNN and spatiotemporal models for motion encoding autoencoder and generative adversarial frameworks for unsupervised reconstruction transformer and attention-based models for long-range dependency modeling memory-augmented networks for prototypeconstrained normality learning multimodal fusion architectures and edge-intelligent and conversational AI systems for scalable, interactive deployment. The results demonstrate a performance evolution from early CNN-based classifiers (around 85% AUC) to recent transformer-driven and memory-augmented methods achieving AUC values above 97% on UCF-Crime, ShanghaiTech, CUHK Avenue, and RWF-2000. The review additionally incorporates the MSAD multi-scenario benchmark and the CUVA causation dataset, and provides a methodological caveat on the comparability of AUC scores across heterogeneous supervision paradigms. Key open challenges—dataset imbalance, occlusion, illumination variation, domain generalization, and real-time latency—are mapped to research directions including weakly supervised MLLMs, privacy-preserving federated learning, and edge-optimized transformer pipelines.



