Show HN: Emotive Engine – Animation engine with musical time (not milliseconds) (github.com)

Emotive Engine is a lightweight, TypeScript-ready animation engine released as an npm package (@joshtol/emotive-engine) that drives real-time, emotionally expressive character visuals for AI interfaces using musical time (beats) instead of milliseconds. It combines particle-based emotional visualization, shape morphing, dynamic gestures, audio-reactive beat/frequency detection, and 44 built-in context-aware “semantic performances.” The engine is pure Canvas 2D (no WebGL), zero framework dependencies, tree-shakeable ES modules, ships with TypeScript defs and source maps, and is MIT-licensed with demos showing stable 60 FPS on mobile via adaptive quality. Practical demos include retail assistants, language tutors, healthcare check-ins, voice assistant avatars, and music-synced NPCs; there’s also LLM integration examples for dynamic emotional responses. The key technical innovation is treating musical time as the atomic unit so animations automatically scale with tempo—e.g., a 1-beat bounce is 500 ms at 120 BPM, 667 ms at 90 BPM, 353 ms at 170 BPM—preventing rhythm drift when tempo changes. Performance tuning recommendations (200–500 particles for desktop, 100–200 on mobile), cross-browser support (modern Chrome/Edge, Firefox, Safari, mobile), and built-in beat detection make it immediately useful for multimodal, music-aware AI/ML products. For developers and researchers, this lowers the integration cost for emotionally-synced agents, enabling more natural audiovisual alignment in conversational agents, educational tutors, and interactive media.