Please excuse my ignorance on this matter.
I have ripped a VOB file of a concert DVD including chapter marks with DVD Decrypter.
When I play the VOB file I cannot change chapters.
How can I retain my chapter marks?
Unfortunately, chapter marks that are lost during a rip have to be reinserted by a reauthoring step.
If you saved the text file in the appropriate format (selected in the the DVD Decrypter IFO mode settings), then you can use IFOedit to add them back in a reauthor to a DVD-Video title. Unfortunately you also have to demultiplex the audio and video first before the reauthoring.