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* MKVToolNix GUI: the GUI could abort with an exception on startup while looking for the `mkvmerge` or `mediainfo` executables due to inaccessible folders. Avoids mis-detection of the `.sub` as MPEG program streams. * mkvmerge: VobSub reader: mkvmerge will now probe the `.idx` file during VobSub identification even if the `.sub` file is passed as the source. The latter didn't work correctly with UNC paths after the switch to `boost::filesystem::path` in v74. * all: switched back to using `boost::filesystem` functions for creating directories instead of the ones introduced to work around bugs in `std::filesystem`. * mkvmerge: MP4 reader: mkvmerge will now read Timed Text (FourCC `tx3g`) subtitle tracks & convert them on the fly to Matroska's simple text subtitle format (`S_TEXT/UTF8` text only, no styles).
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