tomasc, thanks once again.
I tried your suggestion, and yes, this seems to work with a standard DVD.
What I now realise I forgot to mention is that most of the DVDs are stored on a network drive, there does not seem to be a facility to 'capture' from anything other than "external or optical drive" other than webcam, screen etc. using this more useful facility - that you suggested.
I thought that I could burn them back to a DVD and try using the usual 'capture' function, as you suggested, but this would be very time consuming considering the number of possible files that I could need for a project.
Unless, once again, I'm missing the finer detail!