[Replying to most recent post for convenience]
Thanks for all the input, good food for thought and experimentation.
It's clear that video formats, conversion, etc. is something of a minefield. Given that I can't get PowerPoint 2010 to satisfactorily play MP4 files (with Quicktime installed) - it stutters unacceptably, though plays fine stand-alone, presumably the PowerPoint 2010 environment isn't working properly with QT. Thus the ability to convert files to .WMV format is essential in any converter.
I can't get Handbrake to create a WMV file - at least I can't see how to get it to do so.
Freemake easily and quickly creates a WMV file, and $9.99 to get rid of the Freemake header and trailer is not unreasonable, though PowerPoint can trim the video anyway.
Real Converter can create WMV but takes an age and all but cooks the CPU.
I haven't yet tried Xilisoft or DVDvideosoft.
Anyone know why PPT 2010 is unable to properly play MP4 files?
Happily running Windows 10 Pro on both desktop and laptop
We have more and more laws, and less and less enforcement