The ogmtools package has dvdxchap which prints out chapter-format for an OGM container.
It's kind of flaky, and has bugs – I don't remember what they were since it's been so long. I wrote my own though, which does the same – with bugfixes.
dvd_info --ogm
CHAPTER01=00:00:00.000 CHAPTER01NAME=Chapter 01 CHAPTER02=00:20:40.000 CHAPTER02NAME=Chapter 02 CHAPTER03=00:41:49.000 CHAPTER03NAME=Chapter 03 CHAPTER04=01:02:40.834 CHAPTER04NAME=Chapter 04 CHAPTER05=01:23:39.668 CHAPTER05NAME=Chapter 05
I actually like this chapter format because mkvmerge can use it.
dvd_info --ogm > chapters.ogm dvd_copy -o video.vob mkvmerge -o video.mkv --chapters chapters.ogm video.vob