A Comparative Study of Emotion Recognition Systems: From Classical Approaches to Multimodal Large Language Models

Featured Application: Emotion recognition in video (ERV) enables practical deployment in human–AI interaction, assistive systems, and intelligent monitoring applications. The review highlights engineering trade-offs among accuracy, robustness, and computational cost, showing that lightweight deep models are well suited to resource-constrained platforms, whereas multimodal large language models support context-aware interaction in cloud-assisted systems. Emotion recognition in video (ERV) aims to infer human affect from visual, audio, and contextual signals and is increasingly important for interactive and intelligent systems. Over the past decade, ERV has evolved from handcrafted features and task-specific deep learning models toward transformer-based vision–language models and multimodal large language models (MLLMs). This review surveys this evolution, with an emphasis on engineering considerations relevant to real-world deployment. We analyze multimodal fusion strategies, dataset characteristics, and evaluation protocols, highlighting limitations in robustness, bias, and annotation quality under unconstrained conditions. Emerging MLLM-based approaches are examined in terms of performance, reasoning capability, computational cost, and interaction potential. By comparing task-specific models with foundation model approaches, we clarify their respective strengths for resource-constrained versus context-aware applications. Finally, we outline practical research directions toward building robust, efficient, and deployable ERV systems for applied scenarios such as assistive technologies and human–AI interaction.