extract subtitles from *.mkv-files on osx

subtitle-extract.txt

lines with $ are commands

### install mkvtoolnix:

$ brew install mkvtoolnix

### list content of the mkv-file:
$ mkvmerge -i mymoviefile.mkv

### what will give you:
File 'mymoviefiel.mkv': container: Matroska
Track ID 1: video (V_MPEG4/ISO/AVC)
Track ID 2: audio (A_DTS)
Track ID 3: subtitles (S_TEXT/UTF8)
Track ID 4: subtitles (S_TEXT/UTF8)
Chapters: 22 entries

### so the subtitle-tracks are number 3 and 4.
### extract all subtitle-tracks into a seperate srt-file / lang
$ mkvextract tracks mymoviefile.mkv 3:sub3.srt 4:sub4.srt