ffprobe video.mkv 2>&1 | grep Subtitle

This will generate something like this:

Stream #0:3(eng): Subtitle: subrip (srt) (default) (forced)
Stream #0:4(eng): Subtitle: subrip (srt)
Stream #0:5(eng): Subtitle: subrip (srt) (hearing impaired)
Stream #0:6(dut): Subtitle: subrip (pgs)

We're looking for a Dutch (dut) PGS subtitle, so that would be stream #0:6 in this example.

Now we can extract this PGS subtitle as a SUP file:

ffmpeg -i filename.mkv -map 0:s:6 -c:s copy -f sup output.sup

(here "0:s:6" stands for stream #0:6 - the pgs subtitle we want)

No you can use Subtitle Edit (only available for Windows, so you will need a virtual machine or a Windows PC) to convert this with OCR to a plain text SRT.

for f in *.mkv; do ffmpeg -i "$f" -map 0:s:m:language:eng "${f%.*}.srt"; done

This assumes you are in the directory where the MKV video files are, and that you want to extract the english subtitles, and that the subtitles are in SRT format. Note that "0:s:m" assumes that you are looking at the first subtitle only!

Say you want to do the same for MP4 files and you're looking for Dutch SRT subtitles, then you can try one of these two:

for f in *.mp4; do ffmpeg -i "$f" -map 0:s:m:language:nld "${f%.*}.srt"; done
for f in *.mp4; do ffmpeg -i "$f" -map 0:s:m:language:dut "${f%.*}.srt"; done

Note the differences and keep in mind that you will need ffmpeg.

To extract all Dutch (nld) subtitles from MP4 files, and save each as filename.nld.srt:

for f in *.mp4; do ffmpeg -i "$f" -map 0:s:m:language:nld "${f%.*}.nld.srt"; done

Or another example, extract all English (eng) susbtitles from MKV files and save them as as filename.eng.srt:

for f in *.mkv; do ffmpeg -i "$f" -map 0:s:m:language:eng "${f%.*}.eng.srt"; done

For reference:

Trailers are called "trailer.mp4" in this example, and the root path of all video directories is "/Volumes/SomeShare/Multimedia/Movies" - replace these with the proper info for your setup.

find /Volumes/SomeShare/Multimedia/Movies -maxdepth 1 -mindepth 1 -type d '!' -exec sh -c 'ls -1 "{}"|egrep -iq "trailer.mp4" ' ';' -print

This one liner will dig through all directories in "/Volumes/SomeShare/Multimedia/Movies".
It will however only go exactly one level deep (-maxdepth 1 -mindepth 1), meaning it will look into "/Volumes/SomeShare/Multimedia/Movies/A Movie/" but not in "/Volumes/SomeShare/Multimedia/Movies/A Movie/Pictures/".
Picking up those that do not have trailer.mp4 in it.

Just posting this here so my friend can copy it straight from here, and maybe its helpful for other that are looking for directories that do not contain a certain file. Eg. missing cover images in your music collection. If that requires 2 files, then you could do something like this:

find /Volumes/AllShares/Multimedia/Music -mindepth 1 -maxdepth 1 -type d '!' -exec sh -c 'ls -1 "{}"|egrep -i -q "cover\.(jpg|png)"' ';' -print

<trailer>plugin://plugin.video.youtube/play/?video_id=XXXXXX</trailer>

This one, found in the movie.nfo file, will cause this error (in the WebUI anyway):

Playback Error
No player found for the requested media.

We can fix this by updating the link to:

<trailer>plugin://plugin.video.youtube/?action=play_video&amp;videoid=XXXXXX</trailer>

Granted, that would be a lot of work if you have a rather big collection of movies.

Of course, here you can use the power of Linux shell commands - assuming you're executing this on a Linux machine (like most NAS devices are):

find ./ -name movie.nfo -type f  -exec sed -i 's/play\/?video_id=/\?action=play_video\&videoid=/g' {} \;

Assuming you're in your movie directory, this will try to find all files names movie.nfo.
This filename is then used to execute sed and replace the text "play/?video_id=" with "?action=play_video&videoid=".
The "\" symbols are added to escape certain special characters.

* note:
if you're not in you movie directory then either go there (cd /path/to/movie/directory) or replace "./" with "/path/to/movie/directory".

Click on your profile icon (top-right of your screen), and select Display.
Scroll to bottom to Libraries and uncheck Display missing episodes within seasons.

(may need a refresh scan of all libraries by JellyFin)

(IP addresses are of course just examples to illustrate)

Location A (192.168.22.x):
We have an OPNSense firewall running a Wireguard server, opened up for one very specific IP address (192.168.22.100) in that LAN.

Location B (192.168.2.x):
We have the Asus router (client) connecting to Location A, so we can reach the specific device located at location A.

OPNSense and the Asus router both show being connected (Wireguard handshake) properly, yet zero traffic went through.
Meaning: traffic from a PC (192.168.2.10) at location B, connected to the Asus, would not route to the IP address (192.168.22.100) on location B.

Note : of course, first makes ure your Wireguard config works. We tested this with Wireguard on a PC and an iPhone before proceeding. Just making sure the config was correct.

After quite a bit of tinkering we found a fix:

In the Asus router we seem to have to add a route ...
Go to Advanced Settings -> VPN -> VPN Director and look at the section at the bottom where we can add rules.

Klik the (+) icon to add a rule.

Set Interface to Wireguard, add an optional description (recommended) and enter the destination IP address (192.168.22.100) at location B.

That did the trick ... 😊 

LunaSea is a great little app for iOS or Android, to monitor your media related services like Sonarr, Radarr, NZBGet etc.
So it sounds only logical to add Jellyfin to that bunch.

These are the steps to get that going:

• 1 - In Lunasea go to settings -> notifications. With each service you can get a "Device".

When clicking the button a Device link is generated which we need.

Example (shortened since the gobbledygook is quite long after /device/):

https://notify.lunasea.app/v1/lidarr/device/dK1...xre_lja

Grab that link and replace the selected service (lidarr in this example) with "custom":

https://notify.lunasea.app/v1/custom/device/dK1...xre_lja

• 2 - In Jellyfin (server) go to Dashboard -> Plugins and make sure "Webhook" is installed.

If not: install it and reboot the JellyFin server!

• 3 - In Dashboard -> Plugins click the 3-dots and select Settings.

• 4 - In the settings window we now click "Add Generic Destination" and scroll down to edit the settings.

Webhook Name: LunaSea (or whatever you want to call it - it's just so you can see what is what)
Webhook URL: paste the modified link we got in step 1.
Notification Type: check whatever you like. I used "Start playback" for testing, so I just have to start a video to see a notification.

Template: I used something super simple for that, which you can modify to your taste. Just make sure the fields "title" and "body" exist and are a string.
The used notation to fill in variable is called Handlebars notation. Webhook variables are listed on the Webhook Github page.

{
  "title": "JellyFin: {{{NotificationType}}}",
  "body": "{{{Name}}}"
}

Tip:
If you like, you can add an image field to include an icon or something like that (on the right of the notification).
The link needs to be accessible on the Internet. This needs to be a PNG (recommended) or JPG. Also recommended to keep those images small 😉 

Example:

{
  "title": "JellyFin: {{{NotificationType}}}",
  "body": "{{{Name}}}",
  "image": "https://example.com/link/to/jellyfin-logo.png"
}

• 5 - Add a request header by clicking "Add Request Header".

If you forget this, you'll get messages like "Unknown Title Unknown Content".

Key: Content-type
Value: application/json

Click "Save" and you should be good to go.
As mentioned before: I did test my notifications with playback start/stop. Would have been cool if the Webhook devs would have added a test button.

Add OverSeerr Assistant to your Chromium based browser (Google Chrome, Microsoft Edge and Opera tested).
This will add this neat little button to quickly request a movie or TV show to JellySeerr.

It nicely indicates if something was already requested, or is available already.