mkvmerge — Merge and extract multimedia streams. More information: <https://mkvtoolnix.download/doc/mkvmerge.ht

Display information about a Matroska file

mkvmerge --identify {{path/to/file.mkv}}

Extract the audio from track 1 of a specific file

mkvextract tracks {{path/to/file.mkv}} {{1}}:{{path/to/output.webm}}

Extract the subtitle from track 3 of a specific file

mkvextract tracks {{path/to/file.mkv}} {{3}}:{{path/to/subs.srt}}

Add a subtitle track to a file

mkvmerge --output {{path/to/output.mkv}} {{path/to/file.mkv}} {{path/to/subs.srt}}