Proper subtitle settings in MKVToolNix, not sure if I know how subs work

[MarioVideo]

Hello,

I have be remuxing some movies sometimes from mkv files, sometimes from BDMV folders and am wondering if I am using the proper subtitle settings. I don't think I have a full grasp on how subtitles work. For example, for Avatar, I am having trouble having the Navi only subtitles to show. On some players, such as Kodi, they only display when the subtitles are disabled, but this is only the case on the shield. When I disable the subs in kodi or VLC on my windows 10 computer, nothing displays. I thought Avatar had the Navi parts hard coded, but that is not the case for obious reasons, but then I realized that on most releases the yellow subtitles with special font would only display when the subtitles where disabled, even though, for some strange reason, this was not the behavior of the file when played in Kodi or VLC on my windows 10 computer. In some players I have to have the subtitles enabled and have a specific "Navi Only" subtitle to get them to display. So, something is off and I think it is my understanding of how subtitles work with mkv files.

For example, every movie file I work with has subs enabled when I import them into MKVToolNix. As such, if I leave things as they are, with the subs enabled and a defaulted sub file, the preferred language or default language subtitle will always play, unless I have defaulted the video player to not show subs by default it its global settings. This is not he behavior I want. I want to enable the movie subtitles if I want them to play, not have them defaulted to be enabled because sometimes I lend out the movie or use the movie on a player with subs enabled by default and I have to disable the subtitles. I would rather have to enable and choose subs on films that need them.

So what I have done is disable but still copy all the subs when I remux them. I have also noticed that if I set a subtitle as the default title it will play even though it is not enabled, which is weird. So I have also removed the default tag. This results in the behavior I want, where I play a movie on any player and the subtitles do not play. If I want, I can then chose and enable any sub I wish. But I wonder if these are the proper settings as, as aforementioned, all the files come with all subtitles enabled by default and with a default subtitle. There must be a reason why they are all set this way.

If anyone can explain the proper way to set things and get things to play a desired way, or point me to a place that can, I would sincerely appreciate it. I hope I am not making poor choices that will cause me to remux all these files again. Thanks in advance!!

[ProWo]

As a quick overview:

Burned-in subtitles are always displayed and cannot be selected by the player.

All other subtitles are included as a separate stream in the video container and can be selected and activated by the player.
If they are marked with a forced flag, they are automatically displayed by the player.
However, this does not work with many TV players.

A special case are the so-called closed captions, which are only used in America. These are displayed automatically and are encoded in the video stream.

[Ennio]

There's much difference on how players act on force-flagged subtitles, and in conjunction to their setup menu configuration and certain other header settings in mkv. Recently there's been talk about it here https://forum.videohelp.com/threads/411032-MKVtoolNix-2-audio-and-2-forced-subtitles. Annoyingly what works for one player doesn't guarantee to do so for another.

As a foolproof solution you can mux a separate SUP track that holds only the so-called "forced-flagged" subtitles. This may require some manual labour. Mux it without force-flag to avoid unwanted/unforeseen player behaviour. You'll always be able to select it with the subtitle button of your remote. Always works.

[MarioVideo]

Thank you both! So, I am not screwing anything up by taking off the defaults and not enabling any subtitles? I assume I can always chose and enable them through the video player. I will take Ennio's advice and just include or name the track that should be used, though sometimes it is hard to find just the foreign parts translated to English, like I did for the Navi parts in avatar. Really these should be labeled as FORCED, but mostly they are not.

[Ennio]

SUPs being "forced" on (UHD)BD can be achieved different ways. Taking your Avatar Na'vi example, it's possible that these particular subtitles are a part of a bigger, "full English" PGS stream. In which they carry a "forced" flag. These can be isolated with Subtitle Edit's SUP editor.

It's also possible that there's a separate PGS stream holding only the Na'vi sups. Often in such cases these sups are not flagged as forced, but can be driven to be displayed by choice of blu-ray menu. For example, when you set BD subtitle menu to "None" the player will show only the Na'vi ones.
Obviously in such a case isolation isn't necessary.

You can find out by demuxing all PGS streams and have a look at them.

[EDIT] Sorry, I overlooked the first "enabling" part. I can't really tell you what this does and how players will react on this flag being set or not.
Maybe more knowledgable people are able to tell what it's for. And surely Mosu - the author of MKVToolNix - can answer this if you'd ask him in his thread at the Doom9 forums. FWIW I always leave this flag to its default "Yes". Never got into trouble.

https://forum.doom9.org/showthread.php?t=175593

[MarioVideo]

Thanks Ennio! I really appreciate your help in clarifying this matter for me! I will ask on the forum, I guess I have to wait 5 days...

[Ennio]

You're welcome. Note that it is not always possible to isolate the "forced" subtitles with whatever software. In my experience, sometimes manual parsing and editing of the sourcefile is required to obtain a "forced only" subtitle track. Which goes for both text- and image-based subtitles, btw. Where obviously simultaneous video-preview can be a big help, if not downright needed.