subtitle-audit

name	subtitle-audit
description	This skill should be used when the user asks "check subtitles", "audit subs", "subtitle font issues", "ASS vs SRT", "missing fonts", "subtitle timing", or wants to analyze subtitle tracks for issues like missing fonts, timing problems, or format limitations.

Subtitle Track Audit

Analyze subtitle tracks for issues including missing fonts, timing problems, format capabilities, and proper tagging.

Subtitle Formats

ASS (Advanced SubStation Alpha)

Capabilities:

• Full styling (fonts, colors, positioning)
• Complex typesetting (signs, karaoke)
• Multiple styles per file
• Precise positioning

Requirements:

• Fonts must be available (embedded or installed)
• Only MKV container fully supports ASS
• MP4 does not support ASS (must hardsub)

SRT (SubRip)

Capabilities:

• Basic text with timing
• Limited styling (some players support HTML tags)
• Wide compatibility

Limitations:

• No font specification
• No precise positioning
• No complex typesetting

PGS (Presentation Graphic Stream)

Capabilities:

• Blu-ray subtitle format
• Image-based (pre-rendered)
• Perfect styling preservation

Limitations:

• Cannot be edited easily
• Large file size
• Text not searchable/selectable

Audit Workflow

Step 1: List Subtitle Tracks

mediainfo video.mkv

Look for Subtitle sections showing:

• Format (ASS, SRT, PGS, etc.)
• Language
• Title/name
• Default/forced flags

Using ffprobe:

ffprobe -v error -select_streams s -show_entries \
  stream=index,codec_name:stream_tags=language,title \
  -of csv=p=0 video.mkv

Step 2: Extract for Inspection

# Extract first subtitle track
ffmpeg -i video.mkv -map 0:s:0 subtitles.ass

# Extract by language
ffmpeg -i video.mkv -map 0:s:m:language:eng output.srt

Step 3: Check ASS Font Requirements

Using Aegisub:

1. Open ASS file in Aegisub
2. Go to View → Fonts Collector
3. Lists all fonts used and availability

Manual inspection: Open ASS file in text editor, look for Style lines:

Style: Default,Arial,48,&H00FFFFFF,...

The second field after style name is the font.

Step 4: Verify Embedded Fonts

For MKV files, check attachments:

mediainfo video.mkv | grep -A 20 "Attachment"

Should show font files (TTF, OTF) if fonts are embedded.

Extract embedded fonts:

mkvextract attachments video.mkv 1:font1.ttf 2:font2.ttf

Step 5: Timing Analysis

Check for issues:

• Subtitles appearing too early/late
• Overlapping subtitle events
• Very short display times

Using Aegisub:

• Open subtitle file
• Check timing column for irregularities
• Look for negative durations or overlaps

Common Issues

Missing Fonts

Symptoms:

• Subtitles render in wrong font
• Missing characters (boxes or blanks)
• Wrong styling/positioning

Solutions:

1. Install required fonts system-wide
2. Use font manager (FontBase) for temporary activation
3. Embed fonts when muxing MKV

Wrong Language Tag

Symptoms:

• Player selects wrong subtitle track
• Language filtering doesn't work

Fix with MKVToolNix:

mkvpropedit video.mkv --edit track:s1 --set language=eng

Timing Offset

Symptoms:

• All subtitles early or late by same amount

Fix:

# Delay subtitles by 2 seconds
ffmpeg -i input.srt -itsoffset 2 -i input.srt -c copy output.srt

Or use Aegisub: Timing → Shift Times

Container Compatibility

MKV: Full ASS support, can embed fonts MP4: No ASS support, SRT only (basic), or must hardsub WebM: Limited subtitle support

Muxing Subtitles

Add to MKV

# With MKVToolNix
mkvmerge -o output.mkv input.mkv subtitles.ass

# With ffmpeg
ffmpeg -i video.mkv -i subtitles.ass -map 0 -map 1 -c copy output.mkv

Set Language and Default

mkvmerge -o output.mkv input.mkv \
  --language 0:eng --default-track 0:yes subtitles.ass

Embed Fonts

mkvmerge -o output.mkv input.mkv subtitles.ass \
  --attach-file font1.ttf --attach-file font2.ttf

Quick Reference

Format	Styling	Fonts	Container Support
ASS	Full	Required	MKV only
SRT	Basic/None	N/A	Most containers
PGS	Image-based	N/A	MKV, M2TS
VobSub	Image-based	N/A	MKV, AVI

Font Collection

When distributing ASS subtitles:

1. Collect fonts using Aegisub's Font Collector
2. Embed in MKV as attachments
3. Test on clean system without fonts installed

Tools

• Aegisub: Subtitle editing, font collection, timing
• MKVToolNix: Muxing, track properties, font embedding
• ffmpeg: Extraction, basic manipulation
• FontBase: Font management without installation

Additional Resources

• ${CLAUDE_PLUGIN_ROOT}/references/tools.md - Tool recommendations
• ${CLAUDE_PLUGIN_ROOT}/references/encoding-commands.md - Subtitle extraction/muxing commands