Like many others, I was very happy that Plex started allowing differentiation of subtitles by language and allowing forced as a clear option…kudos to the dev team for that. With that in mind, how difficult would it be/would anyone else like an option…to have a checkbox to always play forced subtitles?
The default is to display forced subtitles. You have to set the flag so PMS knows which subtitle to use.
For media in MKV enclosures, check out MKVToolNix, https://mkvtoolnix.download/.
Using the Header Editor, you can set the Forced flag for subtitles. Plex will pick this up and display the subtitles.
You can also set the Forced flag when re-muxing in the Multiplexer section.
For mp4 containers, you can use Subler on a Mac, https://subler.org/. There’s surely a Window tool as well, just not aware of one.
It sounds like you’re saying I need another piece of software to do what I’m asking. It’s possible that i’m misunderstanding what you mean, so let me use a real example and you can tell me what i’m doing wrong.
I have “Kill Bill: Vol. 1” in MP4 with two SRT files; one a full English subtitle and the second Forced English for foreign language. When Plex reads The Kill Bill Folder, it detects that Kill Bill is in English, so based on Plex’s Subtitle Rules it does not show the forced foreign srt.
If I tell Plex to “Automatically select audio and subtitles tracks”, which I was using for a while, further problems arise as, for some reason (and here I will take the blame) the audio tracks don’t always register the language. In this scenario, a lot of movies will use the Eng SRT file as default; an issue I’m also trying to avoid.
I would rather have a setting/checkbox that, if possible, would always play the forced subs since the whole point of forced subs is that they always play regardless of what the language is. A more complicated idea would be to do a check of the forced language to the audio language but that still doesn’t solve the unknown language problem.
Hopefully this clarification explains better as to what issue i’m trying to solve. Again, if you’re saying that i need external software to solve it, I get that. I was hoping to avoid it as I’m sure I’m not the only person with this issue. I don’t object to external solutions/answers. We asked for better subtitle recognition, including forced, and got it. On the other hand I finally caved and got Webtools to send my friends Playlist (MCU, DCEU, Realer than Real, Middle Earth etc). I’d rather not do that again if possible.
I believe I misunderstood. You have external subtitles in the same folder as the movie.
I was talking about embedded subtitles, in the MP4 or MKV container along with the audio & video tracks. For embedded subtitles you can set a “forced” flag, which Plex will honor. However, you need another piece of software to set the flag.
Regarding external subtitles, according to Local Media Assets – Movies, Plex should pick up “forced” in the subtitle name.
From the “External Subtitles Files” section:
Tip!:”forced” is a special tag which make the subtitle enabled even if it does not necessarily follow the rules set in your server’s language settings. Normally used for subs which only contain the translation for foreign parts.
I have not tried external forced subtitles. I have used external non-forced subtitles w/o issue.
If you’re not already, suggest you strictly follow Plex’s naming conventions. Plex can be picky at times.
Also, you can use the tools mentioned previously to edit the settings in your media, so that the embedded audio displays the correct language in Plex. This probably doesn’t matter WRT forced subtitles (at least the way I read the documentation), just an FYI.
I ran a quick test. Plex does pick up the forced external subtitles.
I used this naming convention:
/Movies
/Avatar (2009)
Avatar (2009).mkv
Avatar (2009).eng.forced.srt
Plex picks up and plays the subtitles correctly:
The user can override, but the default is to play the forced subtitles.
At a minimum, you’ll need to re-scan the library so Plex picks up the added subtitle file. If (when) you rename directories and/or files to conform to Plex naming conventions, you’ll need to perform the Plex Dance.
I’ve been using proper named conventions since I recommended it years ago 
You’ll have to tell me what other settings you are using for external srts for it to default to them because I took Kill Bill out of my library and when I put it back in I saw no change. I defaulted none. I used to use mostly mkv’s but have been using mp4’s lately. I like the flexibility to create multiple subtitle files. I use eng.srt(for me mostly), eng.SDH.srt(for my best friend), and eng.forced.srt often and I don’t want to have to recompile a significant number of my vids if possible. As of this moment, i’ll just keep setting forced subs manually, but it would be nice if i didn’t have to.
I just retried it with a mp4 movie and Plex enabled the external subtitles. I wanted to make sure it wasn’t a MKV vs MP4 issue. I tested twice, once with embedded subtitles and once without. Plex enabled the external subtitles both times. Details below.
This seems like a PMS, not client, issue. However, I did check with Plex Media Player (Windows 10), Nvidia Shield, and Android phone clients. They all show the external forced subtitles set automatically.
Here’s my library & server settings. These are the ones that seemed applicable. If there’s something else let me know.
Library Settings
Everything checked except "Skip extras which aren't trailers"
Collections = Disabled
Scanner = Plex Movie Scanner
Agent = Plex Movie
Cast List Source = The Movie Database
Ratings Source = Rotten Tomatoes
Plot Summary Source: The Movie Database
Country = United States
Server Settings
General
Version 1.12.0.4829 on Synology DS918+
Version 1.11.3.4803 on Nvidia Shield TV Pro
Agents - Movies - Personal Media
Both checked, listed in this order
Personal Media
Local Media Assets (Movies)
Agents - Movies - Plex Movie
Both checked, listed in this order, others not checked
Local Media Assets (Movies)
Plex Movie
Agents - Movies - The Movie Database
All three checked, listed in this order, Fanart.tv fourth & not checked
Local Media Assets (Movies)
The Movie Database
Plex Movie
MP4 Test Details
Used “Young Frankenstein” which is in my library, and does not have an external subtitles file. The mp4 file did have embedded subtitles (english, non-forced). I ran the test twice, once with embedded subtitles and once without. The results were the same, that Plex enabled external forced subtitles by default.
Full Disclosure: Young Frankenstein does not have forced subtitles (at least my DVD version). I took a SRT file from another movie, renamed it to “Young Frankenstein (1974).eng.forced.srt” and put it in the directory with the movie. Obviously the text did not match the dialog, but Plex picked up the file correctly and displayed the text correctly on-screen. Thought I’d mention it in case you have Young Frankenstein in your collection and noticed it does not have forced subtitles.
Test One - with embedded subtitles
- Removed Young Frankenstein from library.
- Performed Plex Dance to remove traces from system.
- Returned YF to library, along with external forced subtitle file.
- Scanned Library Files.
- Confirmed Plex enabled external forced subtitles by default.
Test Two - without embedded subtitles
- Removed YF from library.
- Performed Plex Dance to remove traces from system.
- Muxed out existing embedded subtitles from movie.
- Returned YF to library, along with external forced subtitle file.
- Scanned Library Files.
- Confirmed Plex enabled external forced subtitles by default.
