MakeMKV users could face such kind of issue: a Blu-ray Disc is successfully ripped into MKV with original video quality, and it plays well with WD TV Live Hub (or whatever HD media player), just not any subtitles are displayed on HDTV. Well there are rare HD media box that plays the original Blu-ray subtitles (PGS encoded .sup file) in MKV container- not an HD media player is meant to play ripped Blu-ray movie.
To have the subtitles displayed correctly, you’ll have to convert the PGS subtitles to SRT or other external subtitles format or rip the Blu-ray again with displayable subtitles. Here’s a decent free tool for extracting/converting PGS subtitles from MKV: SubtitleEdit
How to convert PGS to SRT from MKV video:
1. Open up Subtitle Edit, follow “File>>Import subtitle from Matroska file…” and browse to the MKV source video.
2. Select desired pgs subtitles from MKV.
3. Choose an OCR method to recognize and convert the PGS image subtitles. Click “OK” after OCR proof completed.
4. Select “SubRip(*.srt)” as output format and click “Unbreak”.
Now you have successfully converted PGS to SRT. Name it as the MKV file and put the SRT subtitles into the folder that contained MKV video. The next time you play the MKV there will be subtitles on HDTV.
Optional way converting SRT subtitles for MKV- use Bytecopy to rip .srt subtitles directly from Blu-ray Disc, in that way you get multiple subtitles at one rip.