OK, thanks JJ. I'm pretty new to DVD authoring so I may be making my task more complicated than necessary. I'll describe what I was trying to do, in case anyone can give me any pointers on alternative methods.
I authored a 50 minute DVD in MemoriesOnTV. I'd made that with 24 short chapters, allowing me to add a soundtrack to each one. I burned that and it' plays fine. But MoTV has various weaknesses, and I decided I'd like to try remaking it in Movie Maker. As a bonus that will also help me to get more familiar with MM. So to get started I took the first VOB file from the VIDEO_TS folder that MoTV had created (the one after the small 'menu' VOB) and changed its extension to MPG, (as MM apparently cannot import VOB) and imported it into MM. Using that as a 'clip', I can play it in MM OK. But, although I think I should be able to mute its sound, I can't get that facility to work. So that's why I went back to ConvertXtoDVD to re-convert, this time removing audio.
Terry, West Sussex, UK