CINELERRA-GG supports the .udvd format of DVDs, so you can create subtitles on the timeline and then save them as .udvd files. For how the subtitle tool works see: SubtitlesThe subtitle format for Blu-Ray is PGS with a .sup extension which CinGG does not support. It is an image format (also 3D) so it can be created, converted and extracted only via specific OCR. You can use external programs like ffmpeg; SubTitle Editor; MKVToolNix; etc.
The CINELERRA-GG Community, 2021