Mike, first I must write this must not have DRM. If it's from say the BBC with the usual DRM then you have issues beyond conversion.
Anyhow, does it play in VLC Player? If it does, use that to save in some other more open encoding. This is not an offer on how to use VLC Player. After that save you can use Handbrake or your usual tools to make the Video DVD.
It does probably have DRM and is from the BBC. I thought I'd bought a DVD from the BBC Store but it was a digital download which is not much use when a few of us want to watch it. Is there any way around the DRM? VLC won't play it.
Wait, did you just ask me "help me jack this car?"
Please don't ask me such a thing. I write apps, have worked on video projects and well, please don't ask me this. You can google how to do such things, and if it's not worth paying for, well, it's not worth doing.
Sorry, my understanding is that I've paid the BBC for this video that I thought was a DVD and therefore I've a right to save it on a DVD. I'm unlikely to do this again so I don't want to pay out further good money for an app that I just won't need again. My apologies, however, if my request offends you.
Then you have the discussion with who you bought this. I can't guess how you play it but on a Mac, use a screen recorder then put that on your Video DVD with the tools you use to make Video DVDs.
How to make a Video DVD on a Mac is something well done on the web. Same about screen recording.
PS. Adding with edit. Remember a Video DVD is all of 480p (see Wikipedia) so the result is going to be somewhat horrible compared to BluRay or streaming. But at least it's possible to convert and get it to Video DVD. Yes, it will try the user's patience.