So, I was doing another pass at 'what exactly can encode those PGS streams?' and found this little project: https://github.com/subelf/Spp2Pgs --desc---- Spp2Pgs Converts general subtitles to HDMV PG streams. In other words, converts .ass files to .sup files. The project generates a command line application and a CLR dll file. Core of them is a static library, libspp2pgs. An external dll, xy-VSSppf, is introduced to deal with subtitle files. It's based on a forked version of xy-VSFilter, rendering and providing subtitles in a more easy way. Here is a breif description for all the four parts. Spp2Pgs*.exe An executable converts subtitles to .sup files. Usage: Spp2Pgs -i "X:\Saya1011con.ass" -s 1080 -r 23 "X:\Saya1011con.sup" Type Spp2Pgs -h for more help. libspp2pgs & Spp2PgsNet*.dll The core and its CLR library wrapper for .NET framework applications. Three classes play the main role: PgsEncoder, encoding and writing a pgs file. FrameStream, reading subtitles and rendering subtitles into image. Spp2Pgs, an entrance for all other things. Also reading images from FrameStream and sending them to PgsEncoder. --- It seems to be Windows-based (at least build files are *.vcxproj), and has some x86 asm (yasm) functions, but better than nothing, I guess ... This specific fork was not updated in four years (since 2016), so some subtle (!) bugs may exist .... For license it says: GPL-3.0 License Found this one via google and this forum post from 2019: http://forum.doom9.org/showthread.php?t=176899 Also found subtitler program written in C#/.Net (so it sorta run under Linux/Mono): https://nikse.dk/SubtitleEdit/Help#linux But I have no idea how (if at all) it can be compiled under Linux .. (Arch package basically repackages binary file). Found via https://unix.stackexchange.com/questions/278001/open-hdmv-pgs-subtitles-in-g... Also there was KDE5 based subtitle editor with some speech recognition, but apparently it was archived by developer last year: https://github.com/maxrd2/SubtitleComposer Ah, no I'm blind , it was moved into KDE! https://invent.kde.org/multimedia/subtitlecomposer/-/commits/master So, some interesting findings, but making any of them to work (at least on my machine) will be ..non-trivial.