I found it: with video files that contain subtitles (e.g. as a separate track), there is an option to toggle subtitles during playback in JRemote.
For much of my media, it's all particles pointing to .mpls files. In those cases, the subtitle toggle is not available. Saves a TON if disk space since I do full backups and then use particles to point to eg individual episodes.
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Another question - does JRemote support mp4/HVEC encoding? I have several files of that container and codec, and while audio plays fine, the video just shows the Apple Quicktime logo centered and on a black screen.
this is for local playback as well.
Thanks