I finally got around to working on a VobSub parser for my subtitle editor. VobSub is the subtitle format you find on DVDs by the way.
It's a lot of fun to write these kind of parser, but unlike the PGS parser (Bluray format) I wrote, there is no official documentation for it, so I have basically been peeking at the parser code for SubtitleEdit.
The code is coming along nicely. It can now read and parse the 2048 byte data blocks.
https://github.com/vkbo/Subtle/blob/vobsub-support/subtle_gui/formats/vobsub.py