mkv-strip-tracks

name	mkv-strip-tracks
description	Remove unwanted tracks (audio, subtitle, video) from a Matroska container and save a new, smaller file. Use mkvmerge syntax (-a, -s, -d to keep tracks; -A, -S, -D to drop all of a type). Use when the user says "remove this audio track", "drop all subtitles except English", "keep only this video and audio", "make this file smaller". No re-encode.
disable-model-invocation	false
allowed-tools	Bash(test *), Bash(which *), Bash(mkvmerge *), Bash(mkdir *), Bash(ls *), Bash(dirname *), Bash(basename *), Bash(stat *), Read, Write

MKV Strip Tracks

Selectively keep or discard audio, subtitle, and video tracks in a Matroska container using mkvmerge. Produces a new MKV with only the requested tracks; original is preserved. No re-encoding.

When to use

• User wants to drop unwanted audio or subtitle tracks from a multi-language file
• Reduce file size by removing all subtitles, or all but one audio track
• Clean up a master file before distribution (keep video + one audio + one subtitle)

Inputs to gather

• File — path to source MKV (required)
• Keep audio tracks — comma-separated list of track indices (e.g., 1,2) or language codes; OR -A to drop all audio (optional)
• Keep subtitle tracks — comma-separated list (e.g., 3,4) or -S to drop all subs (optional)
• Keep video tracks — track index (usually 0) or -D to drop all video (rare) (optional, default: keep track 0)
• Output path — where to write the new MKV (optional, default: <original-name>.stripped.mkv in same dir)

Procedure

1. Check mkvtoolnix is installed

if ! command -v mkvmerge >/dev/null; then
  echo "mkvtoolnix not installed. Install: apt install mkvtoolnix"
  exit 1
fi

2. Build the mkvmerge command

mkvmerge uses track-selection flags:

Flag	Effect
-d 0	keep video track 0
-a 1,2	keep audio tracks 1 and 2
-s 3	keep subtitle track 3
-A	drop all audio
-S	drop all subtitles
-D	drop all video

Example: keep video 0, audio 1, subs 3–4:

mkvmerge \
  -d 0 -a 1 -s 3,4 \
  -o "$OUTPUT" "$FILE"

3. Validate tracks exist

Before running mkvmerge, query the source with mkvmerge -i "$FILE" to verify all requested track indices exist. Warn if a track is missing.

4. Show the user the command

Print the full mkvmerge invocation and ask for confirmation (especially if many tracks will be dropped).

5. Run and report

mkvmerge -d 0 -a "$AUDIO_TRACKS" -s "$SUB_TRACKS" -o "$OUTPUT" "$FILE"

After completion, show:

Source    : path/to/in.mkv (12.5 MB)
Output    : path/to/in.stripped.mkv (3.2 MB)
Removed   : audio track 2, all other subtitles
Reduction : 74%

Output / side effects

• Creates a new MKV file at the specified output path.
• Original file is untouched.
• No re-encoding; mkvmerge copies streams as-is.
• The output file is always a new file — mkvmerge cannot edit in-place.

Notes

• mkvmerge is fast and non-destructive compared to ffmpeg, which would require re-encoding if stream-copy alone fails.
• Track indices refer to the physical track order in the file, shown by mkv-track-list. Not all indices are sequential (e.g., if you dropped a track earlier, indices don't shift).
• Language-based selection (e.g., -a eng) is more portable than track indices if the MKV has proper language tags. mkvmerge supports ISO 639-2 codes.
• If the user wants to keep multiple tracks but doesn't know the indices, run mkv-track-list first.
• Chapters, attachments, and global metadata are preserved in the output by default; mkvmerge can also strip these with additional flags if needed (e.g., --no-chapters).