Ffmpeg Metadata

Ffmpeg Metadata

Context: $ARGUMENTS

Quick start

• Set title/artist/year: → Step 1 (pick "set tags") → Step 2
• Add chapter markers: → Step 1 (pick "chapters") → Step 2
• Embed cover art / thumbnail: → Step 1 (pick "cover") → Step 2
• Set audio language / stream title: → Step 1 (per-stream tags) → Step 2
• Mark subtitle default/forced: → Step 1 (disposition) → Step 2
• Strip all metadata: → Step 1 (strip) → Step 2
• Attach font to MKV for ASS subs: → Step 1 (attach) → Step 2
• Always verify after: → Step 3

When to use

• Authoring final deliverables where titles, artists, years, comments must be embedded.
• Adding chapter markers so players (QuickTime, VLC, Plex, iOS) show a chapter list.
• Embedding cover art / poster frames in MP3, MP4/M4A, MKV, FLAC.
• Tagging audio/subtitle streams with correct ISO 639-2 language codes so players auto-select the right track.
• Marking a subtitle track as default and/or forced.
• Stripping identifying metadata before publishing (privacy).
• Attaching fonts to MKV files so ASS subtitle styling renders correctly on other machines.

Step 1 — Pick the operation

Decide which category your task falls in. Each maps to a different flag set.

All of these should use -c copy — changing metadata never requires re-encoding.

Step 2 — Build the command

Set container tags (MP4)

ffmpeg -i in.mp4 -c copy \
  -metadata title="My Video" \
  -metadata artist="Alice" \
  -metadata year=2026 \
  -metadata comment="Rendered 2026-04-17" \
  out.mp4

Set per-stream tags (MKV)

ffmpeg -i in.mkv -c copy \
  -metadata:s:a:0 language=eng -metadata:s:a:0 title="English 5.1" \
  -metadata:s:a:1 language=fra -metadata:s:a:1 title="Français Stereo" \
  -metadata:s:s:0 language=eng -metadata:s:s:0 title="English SDH" \
  out.mkv

Stream specifiers: s:v:0 (first video), s:a:1 (second audio), s:s:0 (first subtitle), s:t:0 (first attachment in MKV).

Add chapters from an ffmetadata file

Create chapters.txt (FIRST line must be ;FFMETADATA1):

;FFMETADATA1
[CHAPTER]
TIMEBASE=1/1000
START=0
END=60000
title=Intro
[CHAPTER]
TIMEBASE=1/1000
START=60000
END=180000
title=Main
[CHAPTER]
TIMEBASE=1/1000
START=180000
END=210000
title=Outro

Apply:

ffmpeg -i in.mp4 -i chapters.txt -map_metadata 1 -map_chapters 1 -c copy out.mp4

Extract existing chapters

ffmpeg -i in.mp4 -f ffmetadata chapters_out.txt

You can edit the resulting file (change titles, times) and re-apply with the command above.

Embed cover art

MP3:

ffmpeg -i in.mp3 -i cover.jpg \
  -map 0:a -map 1:v -c copy \
  -id3v2_version 3 \
  -metadata:s:v title="Album cover" -metadata:s:v comment="Cover (front)" \
  -disposition:v:0 attached_pic \
  out.mp3

MP4 / M4A:

ffmpeg -i in.m4a -i cover.jpg \
  -map 0 -map 1 -c copy \
  -disposition:v:1 attached_pic \
  out.m4a

MKV (via attachment):

ffmpeg -i in.mkv -attach cover.jpg \
  -metadata:s:t:0 mimetype=image/jpeg \
  -metadata:s:t:0 filename=cover.jpg \
  -c copy out.mkv

Attach a font to MKV (for ASS subtitles)

ffmpeg -i in.mkv -attach arial.ttf \
  -metadata:s:t:0 mimetype=application/x-truetype-font \
  -metadata:s:t:0 filename=arial.ttf \
  -c copy out.mkv

Disposition — default / forced subtitle

# ADD flags (keeps any existing)
ffmpeg -i in.mkv -c copy -disposition:s:0 +default+forced out.mkv

# REPLACE flags (drops everything else)
ffmpeg -i in.mkv -c copy -disposition:s:0 default out.mkv

# CLEAR all flags on a stream
ffmpeg -i in.mkv -c copy -disposition:s:0 0 out.mkv

Strip all metadata + chapters

ffmpeg -i in.mp4 -map 0 -map_metadata -1 -map_chapters -1 \
  -c copy -fflags +bitexact -flags:v +bitexact -flags:a +bitexact \
  out.mp4

The +bitexact flags also suppress the automatic encoder=Lavf... tag ffmpeg adds.

Step 3 — Verify with ffprobe

After writing metadata, confirm it stuck:

# All format + stream tags, JSON
ffprobe -v error -show_format -show_streams -show_chapters -of json out.mp4

# Just the title
ffprobe -v error -show_entries format_tags=title -of default=nw=1:nk=1 out.mp4

# Per-stream language tags
ffprobe -v error -show_entries stream=index,codec_type:stream_tags=language,title \
  -of compact out.mkv

# Disposition flags
ffprobe -v error -show_entries stream=index,codec_type:stream_disposition=default,forced,attached_pic \
  -of compact out.mkv

# Chapters only
ffprobe -v error -show_chapters -of json out.mp4

If a tag is missing, check: (a) container supports that key, (b) you used -c copy (re-encoding sometimes drops unsupported tags), (c) -map_metadata wasn't set to -1.

Gotchas

• -c copy is required for metadata-only edits, otherwise ffmpeg re-encodes (slow, quality loss).
• MP4 uses a fixed tag vocabulary — title, artist, album, album_artist, composer, date/year, comment, genre, track, disc, copyright, description, synopsis, show, episode_id, network, lyrics, performer. Arbitrary keys silently drop.
• MKV is permissive — accepts any free-form key; great for custom tagging.
• MP3 maps ffmpeg keys to ID3 automatically (title→TIT2, artist→TPE1, album→TALB, date→TDRC, etc.). Use -id3v2_version 3 for maximum player compatibility.
• Cover art in MP3 needs -disposition:v:0 attached_pic or players ignore it.
• Cover art in MP4 is stored in the covr atom; ffmpeg handles this automatically when attached_pic disposition is set on the image stream.
• ffmetadata files MUST start with ;FFMETADATA1 on line 1 — no leading whitespace, no BOM.
• CHAPTER TIMEBASE uses fraction form — 1/1000 = milliseconds, 1/1 = seconds, 1/90000 = MPEG-TS ticks. START and END are integers in timebase units.
• Language codes are ISO 639-2 three-letter (eng, fra, deu, spa, jpn, kor, zho). Two-letter codes (en, fr) often fail to match in players.
• encoder=Lavf... sneaks back in even after -map_metadata -1. Add -fflags +bitexact -flags:v +bitexact -flags:a +bitexact to suppress.
• -map_chapters -1 is separate from -map_metadata -1 — chapters are tracked independently, strip both to fully clean.
• -disposition:s:0 +default+forced ADDS, -disposition:s:0 default REPLACES. 0 clears all flags.
• MP4 attached_pic stream ordering — some players (notably QuickTime) want the cover image stream to appear AFTER the main video. Use -map to control order.
• MKV attachments persist through -c copy — that's by design. To remove them, see -map -0:t exclusion.
• -metadata:g KEY=VALUE also works for global tags (equivalent to bare -metadata).
• Per-stream -metadata:s:a:0 applies to OUTPUT stream 0 of type a, after -map reordering. If you remap, recount.

Examples

Example 1: podcast MP3 — title, artist, album, cover

ffmpeg -i episode42.mp3 -i cover.jpg \
  -map 0:a -map 1:v -c copy -id3v2_version 3 \
  -metadata title="Episode 42: Time Travel" \
  -metadata artist="The Pod" -metadata album="The Pod Season 3" \
  -metadata date=2026 -metadata track=42 -metadata genre=Podcast \
  -disposition:v:0 attached_pic \
  out.mp3

Example 2: movie MKV — chapters + per-language audio tags

1. Write chapters.txt (see Step 2).
2. Mux:

   ffmpeg -i movie.mkv -i chapters.txt \
     -map_metadata 1 -map_chapters 1 \
     -metadata:s:a:0 language=eng -metadata:s:a:0 title="English 5.1" \
     -metadata:s:a:1 language=fra -metadata:s:a:1 title="Français 5.1" \
     -metadata:s:s:0 language=eng -disposition:s:0 +default \
     -c copy tagged.mkv
   

Example 3: strip everything for privacy

ffmpeg -i vacation.mp4 -map 0 -map_metadata -1 -map_chapters -1 \
  -c copy -fflags +bitexact -flags:v +bitexact -flags:a +bitexact \
  clean.mp4
ffprobe -v error -show_format -show_streams clean.mp4 | grep -i tag

Example 4: force a subtitle as default + forced

ffmpeg -i in.mkv -c copy -disposition:s:0 +default+forced out.mkv
ffprobe -show_entries stream=index:stream_disposition=default,forced -of compact out.mkv

Troubleshooting

Error: At least one output file must be specified

Cause: -f ffmetadata extraction missing an output path. Solution: ffmpeg -i in.mp4 -f ffmetadata chapters.txt — chapters.txt is the output.

Tag disappears after mux

Cause: Container doesn't support that tag name (common: arbitrary keys on MP4). Solution: Use MKV for free-form tags, or pick a supported MP4 key from the list in references/tags.md.

Cover art doesn't show in player

Cause: Missing attached_pic disposition, OR cover is first video stream when player expects it second. Solution: Set -disposition:v:N attached_pic on the image stream; reorder with -map so the primary video is first.

Chapters silently ignored

Cause: ffmetadata file missing ;FFMETADATA1 header, or wrong TIMEBASE. Solution: First line must be exactly ;FFMETADATA1. TIMEBASE must be N/D (e.g. 1/1000).

Language tag not recognized by player

Cause: Used two-letter code (en) instead of three-letter ISO 639-2 (eng). Solution: Always use three-letter: eng, fra, deu, spa, ita, por, jpn, kor, zho, rus, ara, hin.

encoder=Lavf... keeps appearing

Cause: ffmpeg writes its own encoder tag. Solution: Add -fflags +bitexact -flags:v +bitexact -flags:a +bitexact.

Reference docs

• Read references/tags.md for the ffmetadata format spec, per-container tag catalogs (MP4/MKV/MP3/FLAC/OGG/WAV), ISO 639-2 language codes, disposition flag list, cover-art compatibility matrix, MKV edition entries, and ffprobe verification recipes.

Available scripts

• scripts/meta.py — argparse CLI for all metadata operations (set, chapters, extract-chapters, cover, attach, strip, disposition). Prints the ffmpeg command it runs; supports --dry-run and --verbose. Stdlib only.

Usage examples:

# Set container + per-stream tags
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py set \
  --input in.mp4 --output out.mp4 \
  --tags title="My Video" artist="Alice" year=2026 \
  --stream-tags a:0:language=eng a:0:title="English 5.1" s:0:language=eng

# Add chapters from inline timestamps
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py chapters \
  --input in.mp4 --output out.mp4 \
  --from-timestamps "0:00 Intro" "1:00 Main" "3:00 Outro"

# Add chapters from a pre-written ffmetadata file
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py chapters \
  --input in.mp4 --output out.mp4 --chapters-file chapters.txt

# Extract chapters
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py extract-chapters \
  --input in.mp4 --output chapters.txt

# Embed cover art
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py cover \
  --input song.mp3 --output tagged.mp3 --image cover.jpg

# Attach font to MKV
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py attach \
  --input in.mkv --output out.mkv --file arial.ttf \
  --mimetype application/x-truetype-font

# Set disposition flags
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py disposition \
  --input in.mkv --output out.mkv --stream s:0 --flags "+default+forced"

# Strip everything
uv run ${CLAUDE_SKILL_DIR}/scripts/meta.py strip \
  --input in.mp4 --output clean.mp4