# Video Clipper: Full SDD Implementation Summary

**Date:** 2026-09-21  
**Approach:** Subagent-Driven Development (12 tasks + final review)  
**Total commits:** 23 (0bc1f1e → e4710b4)  
**Test suite:** 31 Vitest + 28 Rust tests, all green  

## Task Description

Implemented the full MVP of a macOS GUI Video Clipper app (Tauri v2 + Svelte 5) across 12 tasks, each with an implementer subagent, task review, and fix rounds as needed. The app enables users to paste a YouTube URL, preview/scrub the video, mark clip regions, and export clips via ffmpeg.

## Changes Made

### Task 1: Project Scaffolding & App Shell
- Tauri v2 + Svelte 5 project with Rust backend
- Data models (`VideoMetadata`, `Clip`, `CookieSource`, `ExportConfig`, etc.)
- Utility functions (`formatTime`, `parseTime`, `getClipColor`) with Vitest tests
- App shell layout with 6 stub components
- CSS theme with custom properties

### Task 2: Dependency Manager & Setup Wizard
- Rust `dependency_manager` service (ffmpeg, yt-dlp, JS runtime, PO token detection)
- Tauri commands with Channel-based install progress streaming
- SetupWizard Svelte component with auto-continue
- **Fix round:** stderr threading for install output, cookie flags on PO token check

### Task 3: Preferences Store
- Svelte 5 rune store with `@tauri-apps/plugin-store` persistence
- Output directory + cookie source preferences
- PreferencesPanel component with gear toggle in toolbar
- **Fix round:** guard saves against uninitialized store

### Task 4: Video Resolver, URL Input & Video Player
- Rust `video_resolver` service (yt-dlp JSON parsing, stream URL extraction)
- `resolve_url` Tauri command with cookie support
- `videoSession` store (reactive session state)
- UrlInput (paste detection, resolve flow) + VideoPlayer (HTML5 `<video>`)
- **Fix round:** validate empty stream_url, clear stale metadata on error

### Task 5: Download Manager & Status Bar
- Rust `download_manager` service with progress parsing
- `start_download` command with Channel events
- StatusBar showing download progress
- Auto-download trigger after URL resolve
- **Fix round:** redirect unused stdout to `Stdio::null()`

### Task 6: Timeline Core
- Canvas-based timeline with `TimelineState`, coordinate mapping
- Playhead rendering, time ticks, placeholder lanes
- Mouse scrubbing, cursor-anchored zoom (wheel)
- 12 Vitest tests for pure functions

### Task 7: Clip Management
- `clips` store (Svelte 5 runes) with CRUD + in/out point marking
- Canvas clip renderer with color-coded regions + drag handles
- `hitTestClip` for mouse interaction
- ClipList component (list, edit, select, delete)
- 7 TDD tests for clip store

### Task 8: Transport Controls & Keyboard Shortcuts
- TransportControls component (play/pause, I/O, skip, frame step)
- Global keyboard handler (Space, I, O, J/K/L shuttle, arrows, comma/period)
- Shared `playback.ts` module for DRY transport logic

### Task 9: Keyframe Index & Frame Navigation
- Rust `keyframe_index` service (ffprobe parsing)
- `extract_keyframes` Tauri command
- Auto-fetch after download, wired to transport buttons (Shift+comma/period)

### Task 10: Waveform Generation & Display
- Rust `waveform_generator` service (ffmpeg audio peak extraction)
- Canvas waveform renderer with zoom-aware peak drawing
- Static placeholder while generating
- **Fix round:** clear waveform data on new download

### Task 11: Thumbnail Extraction & Display
- Rust `thumbnail_extractor` service (ffmpeg frame extraction)
- Adaptive density thumbnails on canvas timeline
- Image caching with `convertFileSrc` (Tauri asset protocol)
- **Fix round:** cache invalidation + temp directory cleanup

### Task 12: Clip Export & Export Dialog
- Rust `clip_exporter` service (lossless/precise, individual/merged)
- ExportDialog component (cut mode, scope, directory, progress)
- 6 Rust tests for ffmpeg command construction
- **Fix round:** temp dir cleanup on merge failure

### Final Review Fixes
- Clear clips on new video load
- WebM precise codec mapping (VP9/Opus)
- Home path `~` expansion via `dirs` crate
- computeZoom zero-range guard
- Timeline viewport reset on media switch
- Shuttle rate reset on new URL

## Follow-Up Items

These were identified in reviews as acceptable for MVP but should be addressed:

1. **Per-frame JPGs → sprite sheets** — Thumbnails use individual files instead of tiled grids; performance concern for very long videos
2. **Stream URL expiry handling** — No auto-re-resolve when streaming URL expires during preview
3. **Auto-export on download complete** — Spec calls for this when user is waiting in export dialog
4. **Merged export overlap trimming** — Overlapping clip ranges not trimmed before merge
5. **Export Selected** — ClipList only has Export All, not Export Selected
6. **Cmd+A select all clips** — Only preventDefault, no implementation
7. **Analysis failure UX** — Silent console.error instead of "Failed to generate" placeholder
8. **Zoom slider** — Only wheel zoom; no slider control
9. **Status bar ETA/export progress** — Minimal status bar info
10. **Dead `ExportEvent::Error` / `DownloadEvent::Error` variants** — Unused enum variants

## Lessons Learned

1. **Svelte 5 rune export limitation** — Can't export individual `$state` variables; must use a single `$state` object pattern (discovered in Task 3, applied throughout)
2. **Pipe deadlock pattern** — Piping both stdout and stderr without reading both causes subprocess deadlock. Fixed in Tasks 2 and 5 with either dual-thread reading or `Stdio::null()`.
3. **Stale state on session transitions** — Multiple tasks needed fixes for stale data (metadata, waveform, keyframes, clips) when loading a new URL. A centralized "new session" reset would prevent this pattern.
4. **ffmpeg `aresample` semantics** — Sets sample rate (Hz), not output length; long videos produce large PCM buffers before bucketing.
5. **SDD review loop value** — Per-task reviews caught real bugs (pipe deadlocks, stale state, missing cookie flags) that would have been expensive to debug later. The final whole-branch review caught cross-cutting issues (clip reset, codec mismatch) that per-task gates missed.