gui-video-clipper/chat-summaries/2026-09-21_15-25-sdd-full-implementation-summary.md

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.