If these are miniDVD's, then the likely cause is that the discs were NOT Finalized in the camera. I would check this aspect out, and just Finalize the discs. That should work.
No, these were not compact DVDs, but had been taken from the camera by cable to a regular DVD burner. John's recommendation that I read Bill's tutorial helped, but it took some further digging to find a reference to MPEG Streamclip. Installing that required that I remove Quicktime and install Quicktime Alternative 1.81. That appears to correct the problem. Streamclip complains that the file is "not standard", but allows me to open it anyway, and as I write this it appears to be successfully converting the file to AVI.
Bill, you make reference in your tutorial about "software is available", I would politely suggest that you add "such as mPEG Streamclip and others".
Thanks for quick responses from both of you.
Ah, did not see that step.
Then, the most likely candidate is that the first VOB, on the problem discs, contains some sort of navigation, that is not 100% DVD-Compliant.
I would use software to rip those VOB's. There are many available. As mentioned in the linked article, the first VOB will contain Menus, navigation, and then the first segment of the MPEG-2 file. PrE (and PrPro, as of CS4.2.1) can Import VOB's, so long as they are 100% DVD-Compliant. Most DVR's, some DVD authoring programs, and a few other devices, do NOT produce 100% DVD-Compliant DVD's. This is just an unfortunate fact of life.