Monitor a directory for new files and automaticaly download subs, retry every 12 hours for new releases.

You can use the CLI to search for subtitles. Maybe set a cronjob ?

Where can i find the cli version?

The CLI is part of the SubDownloader you have installed. So if you have installed 2.0.14, that should be also the cli version.

I downloaded The Mac os x version, there is only one Application

You can call SubDownloader from the command line using this path:
/Applications/SubDownloader.app/Contents/MacOS/SubDownloader -h

Thanks a lot Marco

Would be nice if subdownloader could skip videos that already have subtitles. Because it don't believe it can, I created this bash script which I call twice a day:

############
#!/bin/bash
date
# Go to main video directory. Videos may be in subdirectories.
cd /media/Data/Videos

# Find the newest 20 videos.
newvids=`find . -regextype posix-extended -regex '.*(mp4|mkv|avi)' -type f -printf "%TY-%Tm-%Td %TT %p\n" | sort | tail -n 20 | grep -oE "\./.*" | sed 's/^\.\///' | sed 's/ /\\ /g'`

# Change the bash field separator temporarily to a newline, instead of a space.
SAVEIFS=$IFS
IFS=$(echo -en "\n\b")

for vid in $newvids;
do
  sub=`echo $vid | sed -r 's/(mp4|avi|mkv)$/srt/' | sed 's/ /\\ /g'`
  if [ -e $sub ]
  then
 echo -e "Subs already present for current video. :-)"
  else
       echo No subs yet for $vid so asking subdownloader to get it...
       subdownloader -c -q -V $vid -l eng --rename-subs
  fi
done

# Put the field separator back to a space character.
IFS=$SAVEIFS
##############

It finds the 20 newest videos in a given folder and its sub folders, and looks for an srt file with the same name as the video. If it doesn't find an srt file with the same name as the video, it launches subdownloader to get it.

note: perhaps a flaw in the design of this script: if you download a video from a long while ago, and the creation time of that file is therefore a long time ago, it may not end up in the 20 newest videos. I've limited the amount of videos which it finds on purpose, so that it doesn't keep on trying to find subs for videos it will never find subs for.