feat: add comprehensive README documentation for Frame Analyzer project

README.md

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+# Frame Analyzer
+
+Frame Analyzer is a local-first browser app for pulling a small set of representative stills out of a video. You load a video file in the browser, scan it for scene changes, review the candidate frames, and then copy or download the stills you want.
+
+No backend is required for the app itself. Video processing happens in the browser against a local blob URL.
+
+## What It Does
+
+- Loads a local video file without uploading it to a server
+- Samples the video at a configurable interval
+- Scores sampled moments using a hybrid of histogram shift and pixel change
+- Picks candidate frames across the full duration of the video instead of clustering around one active section
+- Shows thumbnail candidates with timestamps
+- Lets you copy a frame as PNG to the clipboard
+- Falls back to PNG download if clipboard image write is blocked
+- Lets you manually add the current scrubbed frame from the video preview
+
+## How Selection Works
+
+The current frame picker is a two-stage pipeline:
+
+1. The scanner samples the video over time and computes a visual-change score for each sampled moment.
+2. The selector first tries to fill the timeline with one strong candidate per time bucket, then backfills additional high-quality frames while preserving temporal spread.
+
+This is intentionally different from a simple threshold-crossing approach. One-pass threshold gating tends to miss gradual transitions and often returns only one or two frames in videos with slow visual evolution.
+
+## Stack
+
+- React 19
+- TypeScript
+- Vite
+- Native browser video decoding through `HTMLVideoElement`
+- Canvas for analysis and frame extraction
+- Clipboard API for image copy
+- `nginx` for static serving in the containerized deployment
+
+## Running Locally
+
+Requirements:
+
+- Node.js 22 or newer is recommended
+- A Chromium-based browser is the safest target for clipboard image support
+
+Install dependencies:
+
+```bash
+npm install
+```
+
+Start the dev server:
+
+```bash
+npm run dev
+```
+
+Build for production:
+
+```bash
+npm run build
+```
+
+Preview the production build locally:
+
+```bash
+npm run preview
+```
+
+## Usage
+
+1. Open the app and select a local video file.
+2. Adjust scan settings if needed:
+   - sample interval
+   - change threshold
+   - pixel delta
+   - minimum gap between captures
+   - target image count
+   - candidate pool size
+   - analysis size
+3. Run the scan.
+4. Review the candidate gallery.
+5. Copy or download the frames you want.
+6. Use the video scrubber and `Add current` if you want to add a frame manually.
+
+## Deployment
+
+This repo includes CapRover deployment files:
+
+- [captain-definition](./captain-definition)
+- [Dockerfile](./Dockerfile)
+
+CapRover will build the app with Node, generate the Vite production output, and serve the built files from `nginx`.
+
+## Project Structure
+
+```text
+src/
+  analysis/
+    candidateRanking.ts
+    frameDifference.ts
+    scanVideo.ts
+  media/
+    canvas.ts
+    clipboard.ts
+    video.ts
+  types/
+    scan.ts
+  App.tsx
+  main.tsx
+  styles.css
+```
+
+## Important Browser Notes
+
+- Clipboard image writing requires a secure context such as `localhost` or HTTPS.
+- Browser codec support varies. MP4/H.264 is the safest general input format.
+- Exact frame extraction is limited by browser video seeking behavior.
+- The app waits for a rendered post-seek frame before capturing thumbnails or exports, but browser decoding behavior can still vary across engines.
+
+## Known Limits
+
+- This is still a heuristic frame picker, not a frame-accurate editor.
+- Very long videos can take time because the browser must seek and decode many timestamps.
+- Videos with subtle lighting changes, heavy motion, or repeated near-identical scenes may still need manual adjustment or manual frame additions.
+- Safari and Firefox may behave differently from Chromium for clipboard support and media decoding.