VOB2MPG has a problem with certain vob files where within the vob file it encounters a video packet where the stored syncronization timer value (called the STC/SCR value) is zero, or becomes zero. This value is only zero when a (cell) packet belonging to a new (internal) vob id number is encountered. Typically the vob id number within a vob file will remain the same, so the STC/SCR will only be zero for the very first video packet in the vob (file). However, with some vobs there can be packets belonging to more than one vob id, and when a/the vob id change occurs the timer value is reset to zero. When it encounters this the VOB2MPG doesn't handle it properly. Standalone or PC based dvd players will continue playing seamlessly. But the VOB2MPG gets confused and playing the MPG from that point is jerky with some long pauses.
One sees the above condition when sound from the next frame is heard before you get to that frame. It is a technique used in some movies.