Convert DTS audio to AC3 in a MKV file

mkvdts2ac3_helper

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##          Correct use of DTS2AC3 script forked from GitHub         ##
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## Source: https://github.com/JakeWharton/mkvdts2ac3                 ##
## Last edit: 2017-05-30                                             ##
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## I forked the repo and cloned it into my NAS as of today
## Requirement: ffmpeg, mkvtoolnix, rsync

## Demux, re-encode audio, remux
mkvdts2ac3.sh --initial --no-dts --new --wd "." input.mkv
   # --initial: puts the new AC3 track as first audio track
   # --no-dts : drops the DTS audio track
   # --new    : do not replace original file
   # --debug  : shows commands one by one, but have to press ENTER at each command
   # --wd "." : works in current directory instead of /tmp by default
   # It will take a long time, because the DTS -> AC3 process runs at ~1x
   
# --initial sets the newt track before the video track, which is not optimal. 
# Yet I fear not using --initial would result in the converted track being the last one (not optimal either)

# Looking into:
# https://superuser.com/questions/539640/how-do-i-swap-the-first-and-second-audio-streams-in-an-mkv-in-a-linux-based-syst
# This allows swapping the first two tracks, i.e. the new audio track (due to --initial) and the video track (which was first before),
# while preserving all other subtitles tracks.
# PS: not sure how it would behave with more audio tracks, but it works with at least 2!
ffmpeg -i input.mkv -map 0:v:0 -map 0:a:1 -map 0:a:0 -map 0:s -c copy output.mkv