Server Version#: 4.69.1
Player Version#: 6.9 build 14
I have mkv files with build-in srt subtitles. The Plex web-app shows them just fine, but roku does not. Roku is showing all of the available languages that are built in, but no matter what I select, it doesn’t show any. I verified that the global captions setting is turned to “Always On”.
Please help
Built in SRT subtitles with MKV container are showing on my Roku.
Can you try the Plex Preview app instead? You have to log into roku.com and add the channel manually by code “plexpreview”. You’ll receive updates faster by using Plex Preview too.
I would also try re-muxing your file using MKVToolNix.
If both of these fail report back.
Thanks for the reply. Never really tried my hand at re-muxing. So I’ll have to read up on that. For what it’s worth these same files work fine with captions in the plex web app and just playing on vlc locally. I’ll give the plex preview a try. It looks like the only update since the version I have now was released yesterday (Plex for Roku - #307 by ljunkie), and don’t really see anything specifically related to handling captions. But worth a shot.
The Roku is picky on the format of the containers. If anything is off playback usually stops. I am nearly 100% that re-muxing the file with MKVToolNix will fix your issue.
@kegbeach Thanks so much for patiently explaining it to me. I know next to nothing about the anatomy of an mkv video, but MKVToolNix was easy to use. What I found, when opening one of the videos in there, was that the Korean subtitle stream was set as default and “forced”, which I think might have been the issue. When I turned off those settings and made English default (but not Forced), that worked on the roku with direct play. Not sure what Forced means, or why that setting would affect Roku’s ability to play any of the subtitle tracks, but that appears to be the solution. Thanks again for the help.
Remuxing
MKV and MP4 are containers. Think of them as envelopes.
In a container you can have a video track, audio tracks, and subtitle tracks, in various formats.
It is possible for the container to be damaged, but the contents are still OK. It is also possible that the individual tracks are misaligned with each other, which can cause playback problems.
Remuxing copies the selected tracks to a new container and aligns them correctly.
The process is somewhat analogous to having a multi-page letter with a damaged envelope and the pages out of order. Remuxing puts the pages in order and places them in a new envelope.
Subtitles
The “forced” flag means the player should play the track even if subtitles are normally turned off. While any track can have the forced flag set, it is usually applied to subtitle tracks that translate when characters speak a foreign language. For example, in Avatar, when the characters speak Na’vi.
The default flag means that the flagged subtitle track should automatically be selected and played. The forced flag takes precedence over the default flag.
In general, for subtitles, Plex honors the forced flag, but not the default flag.
If a track is flagged as forced, Plex will automatically select it and play it.
Plex players do not automatically play subtitle tracks with the default flag.
Plex remembers your subtitle selections for a given movie/episode. If you select a certain subtitle track, Plex will remember the selection the next time you play the media.
FYI for TV shows: Plex remembers subtitle settings on an episode by episode basis. If you have subtitles enabled on a given episode, then auto play the next episode, you will have to re-enable them. Plex does not automatically carry the subtitle setting forward to the next episode.
Audio Tracks & Default Flag
Plex ignores the default flag for audio tracks. Plex picks the first audio track that matches your account language settings.
Plex will remember the chosen audio track the next time you play the media.
Thanks for the additional info. That was helpful. 
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