Agent skill

omnicaptions-convert

Use when converting between caption formats (SRT, VTT, ASS, TTML, Gemini MD, etc.). Supports 30+ caption formats.

View SKILL.md on GitHub Repository
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Install this agent skill to your Project

npx add-skill https://github.com/lattifai/omni-captions-skills/tree/main/skills/omnicaptions-convert

SKILL.md

Caption Format Conversion

Convert between 30+ caption/caption formats using lattifai-captions.

⚡ YouTube Workflow

bash
# 1. Transcribe YouTube video directly
omnicaptions transcribe "https://youtube.com/watch?v=VIDEO_ID" -o transcript.md

# 2. Convert to any format
omnicaptions convert transcript.md -o output.srt
omnicaptions convert transcript.md -o output.ass
omnicaptions convert transcript.md -o output.vtt

When to Use

  • Converting SRT to VTT, ASS, TTML, etc.
  • Converting Gemini markdown transcript to standard caption formats
  • Converting YouTube VTT (with word-level timestamps) to other formats
  • Batch format conversion

When NOT to Use

  • Need transcription (use /omnicaptions:transcribe)
  • Need translation (use /omnicaptions:translate)

Setup

bash
pip install omni-captions-skills --extra-index-url https://lattifai.github.io/pypi/simple/

Quick Reference

Format Extension Read Write
SRT .srt ✓ ✓
VTT .vtt ✓ ✓
ASS/SSA .ass ✓ ✓
TTML .ttml ✓ ✓
Gemini MD .md ✓ ✓
JSON .json ✓ ✓
TXT .txt ✓ ✓

Full list: SRT, VTT, ASS, SSA, TTML, DFXP, SBV, SUB, LRC, JSON, TXT, TSV, Audacity, Audition, FCPXML, EDL, and more.

CLI Usage

bash
# Convert (auto-output to same directory, only changes extension)
omnicaptions convert input.srt -t vtt           # → ./input.vtt
omnicaptions convert transcript.md              # → ./transcript.srt

# Specify output file or directory
omnicaptions convert input.srt -o output/       # → output/input.srt
omnicaptions convert input.srt -o output.vtt    # → output.vtt

# Specify format explicitly
omnicaptions convert input.txt -o out.srt -f txt -t srt

ASS Style Presets

When converting to ASS format, use --style to apply preset styles:

bash
omnicaptions convert input.srt -o output.ass --style default    # White text, bottom
omnicaptions convert input.srt -o output.ass --style top        # White text, top
omnicaptions convert input.srt -o output.ass --style bilingual  # White + Yellow (for bilingual)
omnicaptions convert input.srt -o output.ass --style yellow     # Yellow text, bottom
Preset Position Line 1 Line 2 Use Case
default Bottom White White Standard captions
top Top White White When bottom is occupied
bilingual Bottom White Yellow Bilingual captions (原文 + 译文)
yellow Bottom Yellow Yellow High visibility

Bilingual Example

If your SRT has two-line captions like:

1
00:00:01,000 --> 00:00:03,000
Hello World
你好世界

Use --style bilingual or custom colors:

bash
# Preset: white + yellow
omnicaptions convert bilingual.srt -o output.ass --style bilingual

# Custom colors: green English + yellow Chinese
omnicaptions convert bilingual.srt -o output.ass --line1-color "#00FF00" --line2-color "#FFFF00"

# Mix preset with custom line2 color
omnicaptions convert bilingual.srt -o output.ass --style default --line2-color "#FF6600"

Custom Color Options

Option Description
--line1-color "#RRGGBB" First line (original) color
--line2-color "#RRGGBB" Second line (translation) color

Common colors: #FFFFFF (white), #FFFF00 (yellow), #00FF00 (green), #00FFFF (cyan), #FF6600 (orange)

Font Size and Resolution

Font size is auto-calculated based on video resolution. Resolution is detected from (priority order):

  1. --resolution argument (e.g., 1080p, 4k, 1920x1080)
  2. --video argument (uses ffprobe to detect)
  3. .meta.json file (saved by omnicaptions download)
  4. Default: 1080p
bash
# Auto-detect from .meta.json (saved by download command)
omnicaptions convert abc123.en.srt -o abc123.en.ass --karaoke

# Specify resolution directly
omnicaptions convert input.srt -o output.ass --resolution 4k
omnicaptions convert input.srt -o output.ass --resolution 720p
omnicaptions convert input.srt -o output.ass --resolution 1920x1080

# Detect from video file (uses ffprobe)
omnicaptions convert input.srt -o output.ass --video video.mp4

# Override auto-calculated fontsize
omnicaptions convert input.srt -o output.ass --resolution 4k --fontsize 80
Resolution PlayRes Auto FontSize
480p 854×480 24
720p 1280×720 32
1080p 1920×1080 48 (default)
2K 2560×1440 64
4K 3840×2160 96

Karaoke Mode

Generate karaoke subtitles with word-level highlighting. Requires word-level timing (use LaiCut alignment first).

bash
# Basic karaoke (sweep effect - gradual fill)
omnicaptions convert lyrics_LaiCut.json -o lyrics_LaiCut_karaoke.ass --karaoke

# Different effects
omnicaptions convert lyrics_LaiCut.json -o lyrics_LaiCut_karaoke.ass --karaoke sweep    # Gradual fill (default)
omnicaptions convert lyrics_LaiCut.json -o lyrics_LaiCut_karaoke.ass --karaoke instant  # Instant highlight
omnicaptions convert lyrics_LaiCut.json -o lyrics_LaiCut_karaoke.ass --karaoke outline  # Outline then fill

# LRC karaoke (enhanced word timestamps)
omnicaptions convert lyrics_LaiCut.json -o lyrics_LaiCut_karaoke.lrc --karaoke
Effect ASS Tag Description
sweep \kf Gradual fill from left to right (default)
instant \k Instant word highlight
outline \ko Outline fills, then text fills

Karaoke Workflow

bash
# 1. Align with LaiCut (get word-level timing in JSON)
omnicaptions LaiCut audio.mp3 lyrics.txt

# 2. Convert to karaoke ASS
omnicaptions convert lyrics_LaiCut.json -o karaoke.ass --karaoke

# Or combine with style
omnicaptions convert lyrics_LaiCut.json -o karaoke.ass --karaoke --style yellow

Python Usage

python
from omnicaptions import Caption

# Load any format
cap = Caption.read("input.srt")

# Write to any format
cap.write("output.vtt")
cap.write("output.ass")
cap.write("output.ttml")

Common Mistakes

Mistake Fix
Format not detected Use --from / --to flags
Missing timestamps Source format must have timing info
Encoding error Specify encoding="utf-8"

Related Skills

Skill Use When
/omnicaptions:transcribe Need transcript from audio/video
/omnicaptions:translate Translate with Gemini API
/omnicaptions:translate Translate with Claude (no API key)
/omnicaptions:download Download video/captions first

Workflow Examples

# Transcribe → Convert → Translate (with Claude)
/omnicaptions:transcribe video.mp4
/omnicaptions:convert video_GeminiUnd.md -o video.srt
/omnicaptions:translate video.srt -l zh --bilingual

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