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cottongin 8ad2f1c800 chore: stage all pending work — caption styling, media server, processing modal, docs, summaries

Includes:
- Extended caption styling (font, shadow, dimmed color, bg toggle)
- Media server, subtitle downloader, VTT parser, processing modal
- Waveform tiers, thumbnail/timeline improvements, transport controls
- Hybrid download model, dependency management, clip export enhancements
- 21 chat summaries, 2 implementation plans, 2 design specs

Co-authored-by: Cursor <cursoragent@cursor.com>

2026-09-22 10:48:16 -04:00

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Styled Burn-In and Granular Export Progress

Date: 2026-09-21 23:00
Task: Apply user's caption style settings to burned-in subtitles via ffmpeg's ASS force_style, and add granular per-clip progress reporting during export.

Changes Made

1. CaptionStyle Model (Rust + TS)

src-tauri/src/models.rs — Added CaptionStyle struct with font_size, text_color, background_opacity, text_outline, position. Added caption_style: Option<CaptionStyle> to ExportConfig.
src/lib/bindings/export.ts — Added matching CaptionStyle interface and captionStyle: CaptionStyle | null to ExportConfig. Added clipProgress event variant to the discriminated union. Added optional onClipProgress callback parameter to exportClips().

2. ASS force_style in clip_exporter.rs

src-tauri/src/services/clip_exporter.rs:
- hex_to_ass_color() — Converts CSS hex #RRGGBB to ASS &H00BBGGRR format.
- opacity_to_ass_back_colour() — Converts 0-1 opacity to ASS alpha-prefixed BackColour.
- caption_style_to_force_style() — Builds the full ASS force_style string from CaptionStyle (Fontsize, PrimaryColour, BackColour, Outline, Shadow, Alignment, MarginV, BorderStyle).
- build_ffmpeg_args_burnin_subs() now accepts Option<&CaptionStyle> and appends :force_style='...' to the subtitles filter when provided.
- parse_ffmpeg_time() — Extracts time=HH:MM:SS.mm from ffmpeg stderr progress output.
- run_ffmpeg_with_progress() — Runs ffmpeg with piped stderr, parses progress lines, and invokes a callback with 0.0-1.0 percent values.

3. Progress Callbacks Throughout Export Pipeline

All four export functions (export_single_clip, export_single_clip_with_subs, export_merged, export_merged_with_subs) now accept progress callbacks. They use run_ffmpeg_with_progress() instead of .output() for the encode step, streaming real-time progress.

4. export.rs Command Handler

src-tauri/src/commands/export.rs — Added ClipProgress event variant with current, total, label, percent. Wired progress callbacks for both Individual and Merged export paths. Passes caption_style through to the exporter.

5. ExportDialog Frontend

src/lib/components/ExportDialog.svelte:
- Populates captionStyle in config from preferences.captionSettings when burn-in is enabled.
- Shows a progress bar with percentage during each clip export.
- Displays note that karaoke word highlighting is preview-only for burn-in.

Files Modified

File	Change
`src-tauri/src/models.rs`	Added `CaptionStyle` struct, added field to `ExportConfig`
`src-tauri/src/services/clip_exporter.rs`	ASS helpers, force_style, ffmpeg progress streaming, progress callbacks
`src-tauri/src/commands/export.rs`	`ClipProgress` event, caption_style passthrough, progress wiring
`src/lib/bindings/export.ts`	`CaptionStyle` interface, `clipProgress` event, `onClipProgress` callback
`src/lib/components/ExportDialog.svelte`	captionStyle in config, progress bar UI, karaoke note

Build Verification

cargo check — passes (only pre-existing warnings)
cargo test — all 43 tests pass
svelte-check — passes (only pre-existing vite.config.ts errors)

Lessons Learned

ASS color format uses BGR byte order with alpha prefix (&HAA_BB_GG_RR), where alpha 00 = opaque and FF = transparent (inverted from CSS).
BorderStyle=4 in ASS gives an opaque background box behind text (like CSS background), vs BorderStyle=1 which uses outline+shadow only.
ffmpeg progress is on stderr, not stdout. The time= field is the key metric for computing encode progress percentage.
For merged exports, progress is reported per-segment during encoding, plus a concat step at the end.

Follow-Up Items

Smoke test burn-in export to verify styled subtitles render correctly.
Karaoke word-by-word animation in burn-in would require converting VTT word timestamps to ASS \k override tags — complex and fragile, noted as preview-only limitation.

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