mkv-extract-track

MKV Extract Track

Pull a single audio, subtitle, or video track out of a Matroska container and save it as a standalone file. Uses mkvextract for speed and fidelity; no re-encoding.

When to use

• User wants to extract an audio track and save as standalone WAV/AAC/FLAC
• Extract subtitle track as SRT or ASS/SSA
• Pull an embedded font or attachment from an MKV
• Get a video stream without audio/subs as separate file

Inputs to gather

• File — path to source MKV (required)
• Track index — the track to extract (required; from mkv-track-list)
• Output path — where to save the extracted track (required; extension matters: .srt, .mka, .aac, .wav, .ass, etc.)

Procedure

1. Check mkvtoolnix is installed

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

2. Determine track type from source

Query the source file:

mkvmerge -i "$FILE" | grep "^Track ID $TRACK_INDEX:" | head -1

Output will indicate the type: video, audio, subtitles, attachments, etc.

3. Validate output extension

mkvextract infers the codec from the source and writes appropriate format. Guide the user:

Source Codec	Suggested Extension
UTF-8 text (subs)	.srt
ASS/SSA (subs)	.ass
AAC audio	.aac or .mka (Matroska audio)
FLAC audio	.flac
PCM / WAV	.wav
H.264 video	.h264
H.265 video	.h265 or .hevc

If the user provides a mismatched extension, warn but allow (mkvextract will write the correct format regardless).

4. Run mkvextract

mkvextract "tracks" "$FILE" "$TRACK_INDEX:$OUTPUT"

Example:

# Extract subtitle track 2 as SRT
mkvextract tracks in.mkv 2:out.srt

# Extract audio track 1 as AAC
mkvextract tracks in.mkv 1:out.aac

# Extract audio track 3 as Matroska audio container
mkvextract tracks in.mkv 3:out.mka

5. Report

Source  : path/to/in.mkv
Track   : 1 (audio, AAC stereo)
Output  : path/to/out.aac
Size    : 12.4 MB
Status  : ✓ OK

Output / side effects

• Creates a new file at the specified output path containing only the extracted track.
• Original MKV is untouched.
• No re-encoding; the track is copied bit-for-bit (lossless).
• For subtitle tracks, mkvextract transcodes to the target format (UTF-8 text → SRT or ASS depending on codec) — this is safe and standard.

Notes

• mkvextract is the fastest way to pull tracks out of an MKV compared to ffmpeg, which would require a full demux-re-encode pipeline.
• If the user wants to extract multiple tracks, run this skill once per track. A batch skill is a future enhancement.
• Subtitle tracks: UTF-8 text subtitles are extracted as SRT by default. ASS/SSA subtitles preserve styling (colors, positioning, fonts) if extracted as .ass.
• Audio tracks: Extracted as the codec found in the MKV (AAC, FLAC, Opus, etc.). No normalization or filtering applied.
• Attachments and fonts can also be extracted with mkvextract attachments and mkvextract fonts — future enhancements.