My knowledge on video formats is less than that of my audio knowledge, not that it was much in the first place lol, but my limited understanding is .vob is the usual format on DVDs you buy, generally speaking anyway, but there are a vast number of video formats, possibly more than audio as best I can see, so rather than me blunder along and risk adding to any confusion, here are a couple of links that list numerous formats with a brief explanation of them, hopefully these can tell you more than I could manage clearly.
http://www.fileinfo.com/filetypes/video (great list with a good break down, but don't get bogged down understanding the lesser known formats, they tell you the most common ones)
http://en.wikipedia.org/wiki/Container_format_(digital)
DVD-Video is another read to aid explaining about this, and also mentions audio within this format, it would appear that what the DVD contains greatly depends on how it is made, eg if a bought DVD was capable of utilising Dolby 5.1 or similar, then the format used on that disk may differ from that used on a disk that did not have 5.1 ability, again no clear answer I'm afraid, there are just so many variables, but I hope these links help clear this up a bit for you.
This Link may help you gain a much deeper understanding on how big a field this is, hence not being able to have conclusive answers, and it gives a reasonable breakdown on each format, and touches on compression when relevant, so it may help you more.
As too audio DVDs, these are most likely to be in .mp3 format, simply because any device that can play audio DVDs are most likely to be using this format, the average CD player wont be able to handle an audio DVD AFAIK, but there may be exceptions, but this is the most common format used here.
You can create VCD's (Video Cd's), most common use of these is converting a home shot video of say a birthday or the like, and burning it too disk for other family members to be able to enjoy it as well, ideal for shorter video's rather than a full DVD, hopefully
This will explain a bit more for you here.
Video compression will tell you more than I am able too here, it's a very complex area depending on what you want to do with such info.
I'm sorry I don't know enough to explain clearer than I have, but hopefully between this and putting all the links together between them you should hopefully get at least some of the answers you need\want.