lai-caption

name	lai-caption
description	Convert between 30+ caption/subtitle formats (SRT, VTT, ASS, JSON, TextGrid, LRC, FCPXML, Premiere, …) and shift timing. Trigger on "convert captions", "SRT to VTT", "转换字幕格式", "shift timing", "ASS styling", "karaoke effect", "导入Premiere", or any caption-format question. Do NOT trigger to fix timing accuracy (`/lai-align`) or translate (`/lai-translate`).
allowed-tools	Read, Bash(laicap:*), Bash(lai:*)

Caption Format Conversion

Convert, shift, and style caption files. Format is auto-detected from file extension.

laicap-convert and lai caption convert are the same command — the former is the shortcut entry-point. For pipeline / non-interactive use, add --direct -Y (direct execution, skip confirmation).

Convert

laicap-convert (== lai caption convert) takes two positional args: input_path and output_path. All styling/rendering keys are flat top-level config (render.*, ass.*), not caption.*.

All examples assume a single <base> (media stem or YouTube ID) reused across the pipeline; outputs land in the current directory.

# <base> = podcast
laicap-convert podcast.srt podcast.vtt

Common pairs:

laicap-convert podcast.aligned.json podcast.srt        # JSON → playback formats
laicap-convert podcast.srt podcast.ass                 # basic → styled
laicap-convert podcast.transcript.md podcast.srt       # Gemini markdown → SRT
laicap-convert podcast.aligned.json podcast.TextGrid   # → Praat

Add -Y for non-interactive runs. Use input_format=srt (top-level flag) to override auto-detection when the extension is wrong.

Shift Timing

laicap-shift podcast.srt podcast.shifted.srt 2.5     # forward 2.5 s
laicap-shift podcast.srt podcast.shifted.srt -1.0    # backward 1 s

ASS Styling

Top-level ass.* keys (see lai caption convert --help for the full list):

laicap-convert podcast.srt podcast.ass \
    ass.font_name="Noto Sans CJK SC" \
    ass.font_size=48 \
    ass.primary_color="#FFFFFF"

Karaoke (per-word highlighting)

Requires word-level JSON input (produced by /lai-align with caption.render.word_level=true, or /lai-youtube with the same flag — the upstream flag populates words arrays in the JSON).

laicap-convert podcast.aligned.json podcast.karaoke.ass \
    ass.karaoke_effect=sweep \
    ass.karaoke_color_scheme=azure-gold

render.word_level scope — default is word-scope (per-word \k / \kf / \ko emission). Only pass render.word_level=false to switch to line-scope (a single override at event start, whole text block animates together — CapCut-style "fade in"). You don't need render.word_level=true to enable karaoke; ass.karaoke_effect alone does it.

• ass.karaoke_effect: sweep (classic karaoke fill), instant (hard on/off), outline (outline-only highlight)
• ass.karaoke_color_scheme (12 presets, each tunes primary/secondary/outline/back): azure-gold, sakura-purple, mint-ocean, gardenia-green, sunset-warm, prussian-elegant, burgundy-classic, langgan-spring, mars-teal, spring-field, navy-pink, apricot-dark
• ass.kinetic_style (orthogonal per-word animation, 15 options grouped by feel):
  • Impact: bounce, pop, shake, pulse, swing
  • Smooth: fade, zoom, rise, typewriter, blur_in
  • Stylized: glow, neon, wave, flicker, stagger

Bilingual ASS

Format selection, typography conventions (line order / color / font-size ratio), and four scenario recipes (learning SRT / social ASS / karaoke / dual-track upload) all live in /lai-translate §Bilingual Delivery Guide — don't duplicate. Minimal one-liner for a bilingual JSON from /lai-translate:

# `<base>.translated.json` is the merged JSON (source + translation) from
# `/lai-translate merge.py --bilingual`.
laicap-convert podcast.translated.json podcast.zh.translated.ass \
    ass.primary_color="#FFFFFF" \
    ass.translation_color="#FFC209"

Add ass.karaoke_effect=sweep ass.karaoke_color_scheme=... for per-word karaoke on the source line.

Speaker Color

ass.speaker_color=... paints dialogue per speaker (needs /lai-diarize output in the source). Accepts:

• "" — disabled (default)
• "auto" — 10-color LattifAI palette (cycles for >10 speakers)
• "#RRGGBB,#RRGGBB,..." — CSV of explicit colors, one per speaker in appearance order

# Host = cyan-blue, Guest = pink — short CSV palette
laicap-convert diarized.json out.ass \
    render.include_speaker_in_text=true \
    ass.speaker_color="#658AE4,#F7C3D9"

Broadcast-Grade Profiles (standardization.*)

standardization.* reflows segments to meet CPL/CPS/duration rules before writing. Useful for delivering SRT/VTT to Netflix-class platforms or tighter YouTube specs.

Fields (all top-level):

• standardization.min_duration / max_duration — segment duration bounds (s)
• standardization.min_gap — minimum inter-segment gap (s)
• standardization.max_lines / max_chars_per_line — line wrapping limits
• standardization.optimal_cps — target characters-per-second for readability
• standardization.start_margin / end_margin — pre/post roll per segment
• standardization.margin_collision_mode — trim (default), drop, …

Ready-made profiles:

# Netflix-ish: 42 CPL × 2 lines, 0.8-7 s
laicap-convert diarized.json out.netflix.srt \
    standardization.min_duration=0.8 \
    standardization.max_duration=7.0 \
    standardization.min_gap=0.08 \
    standardization.max_lines=2 \
    standardization.max_chars_per_line=42 \
    standardization.start_margin=0.05 \
    standardization.end_margin=0.15

# YouTube-ish: shorter cues, narrower lines
laicap-convert diarized.json out.youtube.srt \
    standardization.min_duration=0.5 \
    standardization.max_duration=5.0 \
    standardization.max_chars_per_line=35 \
    standardization.start_margin=0.03 \
    standardization.end_margin=0.10

start_margin / end_margin also benefit karaoke exports (give lyrics breathing room) — combine with the karaoke recipe above.

Supported Formats

Category	Formats (read & write unless noted)
Standard	.srt, .vtt, .ass / .ssa, .lrc, .txt, .md
Data	.json, .tsv, .csv, .aud
Linguistic	.TextGrid, .ttml / .xml
NLE	.fcpxml; .prproj.xml (write-only)

Full list: lai caption convert --help.

Data Preservation

Convert to .json first to keep word-level timing, speakers, and translations — then fan out to delivery formats.

• Word-level timing: JSON, TextGrid, ASS-karaoke only
• Speakers: JSON, VTT, ASS, TextGrid (partial in SRT)
• Full styling: ASS only

Common Issues

Problem	Fix
Unknown input format	Specify input_format=srt (top-level flag, not caption.input_format)
Encoding error	Re-save the file as UTF-8
Karaoke has no highlighting	Source JSON needs words arrays — re-run /lai-align with caption.render.word_level=true, then convert with just ass.karaoke_effect=sweep (no render.word_level needed; default is word-scope)
No parameter named 'caption' / 'input'	For laicap-convert, styling keys are flat (render.*, ass.*) and input/output are positional (input_path/output_path) — there is no caption.* namespace here
Plain text missing timing	Add timing via /lai-align first

Related Skills

• /lai-align — fix timing accuracy (conversion doesn't change timing)
• /lai-transcribe — generate captions from audio first
• /lai-translate — translate before bilingual conversion
• /lai-diarize — add speaker labels for speaker-colored output