Milimo System Architect Skill

As an expert on the Milimo Video system architecture, you understand how the React/Vite frontend communicates with the FastAPI backend to orchestrate the AI Cinematic Studio.

Core Architectural Understanding

1. Split Architecture:

   • Frontend: React 18, Vite, TypeScript.
   • Backend: Python 3.10+, FastAPI, SQLModel (SQLite).
   • Microservice: SAM 3 runs on port 8001 as a separate, isolated backend service for object tracking and segmentation.

2. The God Store Pattern (Frontend State):

   • The application relies on a massive Zustand store (timelineStore.ts) built from 7 slices: Project, Shot, Playback, UI, Track, Element, Server.
   • CRITICAL: Never add new React Contexts for global state. Always add to the appropriate Zustand slice.
   • Performance is maintained via useShallow selectors and transient updates (store .getState() references in useRef for render loops).
   • The timeline relies on a "Magnetic V1" layout: Track 0 (V1) items snap together sequentially. V2 and A1 tracks use free placement (startFrame).

3. Job Management & SSE (Backend/Frontend Sync):

   • Long-running generation/inpainting tasks are offloaded to BackgroundTasks in FastAPI.
   • The backend job_utils.py tracks active jobs in a global mapping and broadcasts progress via Server-Sent Events (SSE).
   • The frontend SSEProvider.tsx listens for progress, complete, error, and cancelled events, syncing status directly to the Shot or corresponding Element.
   • On page load, jobPoller.ts triggers one-shot queries to /status/{lastJobId} to hydrate active state from the database.

4. Multi-Track Playback Loop:

   • Playback is driven by a headless requestAnimationFrame loop in PlaybackEngine.tsx.
   • Audio sync is handled by GlobalAudioManager.ts (Web Audio API) to bypass Safari media tag drift. Do not use <audio> elements for timeline tracks.
   • Video elements (CinematicPlayer.tsx) listen to the store via strict drift-correction thresholds (250ms).

Guidelines for Feature Implementation

• Adding an Endpoint: Create it in the appropriate router domain (projects.py, jobs.py, assets.py, elements.py, storyboard.py). Wire it to schemas.py and database.py.
• Handling Progress: Any task that takes longer than 2 seconds MUST log a Job to the DB and broadcast progress via job_utils.broadcast_progress. Provide actionable progress messages.
• Microservice Integration: When calling SAM 3, do not import its modules. Make HTTP requests via InpaintingManager or TrackingManager to localhost:8001.

Rules

• No Canvas Rendering for NLE: The timeline must remain DOM-based CSS rendering. Do not attempt to rewrite the timeline in HTML5 Canvas.
• Maintain Single Source of Truth: timelineStore.ts dictates the state. Local component state is only for transient UI interactions (e.g. dragging, hover states).
• Graceful Cancellation: All long-running tasks must periodically check active_jobs[job_id]["cancelled"] and raise RuntimeError("Cancelled") to free GPU resources.