Interpreting Multimodal Communication at Scale in Short-Form Video: Visual, Audio, and Textual Mental Health Discourse on TikTok

Short-form video platforms integrate text, visuals, and audio into complex communicative acts, yet existing research analyzes these modalities in isolation, lacking scalable frameworks to interpret their joint contributions. This study introduces a pipeline combining automated multimodal feature extraction with Shapley value-based interpretability to analyze how text, visuals, and audio jointly influence engagement. Applying this framework to 162,965 TikTok videos and 814,825 images about social anxiety disorder (SAD), we find that facial expressions outperform textual sentiment in predicting viewership, informational content drives more attention than emotional support, and cross-modal synergies exhibit threshold-dependent effects. These findings demonstrate how multimodal analysis reveals interaction patterns invisible to single-modality approaches. Methodologically, we contribute a reproducible framework for interpretable multimodal research applicable across domains; substantively, we advance understanding of mental health communication in algorithmically mediated environments.