cottongin
8ad2f1c800
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>
65 lines
4.0 KiB
Markdown
65 lines
4.0 KiB
Markdown
# Styled Burn-In and Granular Export Progress
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**Date:** 2026-09-21 23:00
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**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.
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## Changes Made
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### 1. CaptionStyle Model (Rust + TS)
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- **`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`.
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- **`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()`.
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### 2. ASS force_style in clip_exporter.rs
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- **`src-tauri/src/services/clip_exporter.rs`**:
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- `hex_to_ass_color()` — Converts CSS hex `#RRGGBB` to ASS `&H00BBGGRR` format.
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- `opacity_to_ass_back_colour()` — Converts 0-1 opacity to ASS alpha-prefixed BackColour.
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- `caption_style_to_force_style()` — Builds the full ASS force_style string from CaptionStyle (Fontsize, PrimaryColour, BackColour, Outline, Shadow, Alignment, MarginV, BorderStyle).
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- `build_ffmpeg_args_burnin_subs()` now accepts `Option<&CaptionStyle>` and appends `:force_style='...'` to the subtitles filter when provided.
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- `parse_ffmpeg_time()` — Extracts `time=HH:MM:SS.mm` from ffmpeg stderr progress output.
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- `run_ffmpeg_with_progress()` — Runs ffmpeg with piped stderr, parses progress lines, and invokes a callback with 0.0-1.0 percent values.
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### 3. Progress Callbacks Throughout Export Pipeline
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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.
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### 4. export.rs Command Handler
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- **`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.
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### 5. ExportDialog Frontend
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- **`src/lib/components/ExportDialog.svelte`**:
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- Populates `captionStyle` in config from `preferences.captionSettings` when burn-in is enabled.
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- Shows a progress bar with percentage during each clip export.
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- Displays note that karaoke word highlighting is preview-only for burn-in.
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## Files Modified
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| File | Change |
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|------|--------|
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| `src-tauri/src/models.rs` | Added `CaptionStyle` struct, added field to `ExportConfig` |
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| `src-tauri/src/services/clip_exporter.rs` | ASS helpers, force_style, ffmpeg progress streaming, progress callbacks |
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| `src-tauri/src/commands/export.rs` | `ClipProgress` event, caption_style passthrough, progress wiring |
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| `src/lib/bindings/export.ts` | `CaptionStyle` interface, `clipProgress` event, `onClipProgress` callback |
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| `src/lib/components/ExportDialog.svelte` | captionStyle in config, progress bar UI, karaoke note |
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## Build Verification
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- `cargo check` — passes (only pre-existing warnings)
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- `cargo test` — all 43 tests pass
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- `svelte-check` — passes (only pre-existing `vite.config.ts` errors)
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## Lessons Learned
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- ASS color format uses BGR byte order with alpha prefix (`&HAA_BB_GG_RR`), where alpha `00` = opaque and `FF` = transparent (inverted from CSS).
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- `BorderStyle=4` in ASS gives an opaque background box behind text (like CSS background), vs `BorderStyle=1` which uses outline+shadow only.
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- ffmpeg progress is on stderr, not stdout. The `time=` field is the key metric for computing encode progress percentage.
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- For merged exports, progress is reported per-segment during encoding, plus a concat step at the end.
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## Follow-Up Items
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- Smoke test burn-in export to verify styled subtitles render correctly.
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- 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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