Problem with DLNA subtitle

I use Web Video Caster from an Android smartphone to cast m3u8 to a RPi 1 B+ running OSMC 2017.12-1:

  1. If only m3u8 is casted, the video is displayed correctly.
  2. If m3u8 is casted with webvtt, nothing is displayed. To make Web Video Caster aware of the subtitle, 1st enter the webvtt, then enter the m3u8

webvtt: https://www.iandevlin.com/html5test/webvtt/upc-video-subtitles-en.vtt
m3u8: http://184.72.239.149/vod/smil:BigBuckBunny.smil/playlist.m3u8

The debug log that records trials 1 and 2 is at http://paste.osmc.tv/cilevemaze

Casting the same m3u8+webvtt to a Chromecast device does not have this problem.

Did I misconfigure OSMC ?

Could you tell us if this ever worked with OSMC?

While it might work with Chromecast, Kodi’s implementation of UPnP/DLNA is known to be unreliable.

With older versions of OSMC, the problem already existed

I’ll be unable to replicate your situation but if you tell us how you configured Kodi, perhaps someone will be able to advise you further.

All elements in UPnP/DLNA settings are enabled.

Does this work with Kodi installed on any other platform? I’m not sure upnp is capable of subtitles in Kodi’s implementation.

The same problem appears in Kodi on Windows.
There is one case that subtitle casting does work: video is mp4 and subtitle comes from opensubtitles.org (Web Video Caster allows one to also selects subtitle from this source). In this case, the video and subtitle are displayed correctly.
If video is m3u8 and subtitle comes from opensubtitles.org, nothing is displayed.

Sounds like you should be addressing this issue with Kodi developers as it doesn’t seem to be specific to OSMC.