You may never need to (or want to) play a VOB directly, but for learning DVD authoring, it is a must !!
Particularly the "menu VOB" file, VTS_01_0.vob - which has very strange characteristics when viewed separately without the use of a DVD player. Especially if you have created menu transitions, which are video clips that start as a still image of the menu the user is looking at, and then a short video clip runs a special transition scene to get to the target menu. This is the same thing as video clip transitions in Premiere. Here is a sample menu transition:
The problem seems to be with menu background music. This causes the VOB to contain the still image of the menu, followed by a long series of audio only blocks. Well, the viewers tend to skip right over the audio only blocks as they search for image frames to display.
The main movie VOB files will play normally, just like any other video file.
I have only found two VOB viewers capable of preoperly viewing all the frames in a menu VOB:
1) DirectShow Jukebox Sample - this VOB viewer is free - and is a part of "VOBedit". The only drawback is that it does not play menu background music properly and skips it - however, it does show ALL FRAMES of the VOB, which most viewers simply cannot do. The menu background audio problem exists with ALL the VOB viewers I have tried - except one - Womble's MPEG Video Wizard.
I have no idea where this can be downloaded separately, and there is NO info on this on the web - not anywhere. But it works perfectly, and unlike many other utilities that will open and supposedly "preview" VOB files, this one does not mess up on the menu VOB files, even when single-stepping through them. To use, just start up VobEdit, open a VOB file, then click Edit/Preview . . .
Video Redo opens VOB files, lets you set IN and OUT points, and converts the selected section to MPEG-2. It views movie VOB files just fine - but is a disaster at viewing menu VOB files.
2) Womble MPEG Video Wizard - the only "true" VOB viewer. It will show you each fram as they occur, in sequence, and will play the background music if the menu has any. However it is expensive, because it is not made to just view VOB files - it is an entire video editing package.