I tried the live DVD from which I installed C7.
I meant to use a live DVD from some other distro so that it had differently compiled drivers - the idea was to eliminate (or otherwise) the drivers from CentOS 7.
It would not do videos at all. It claimed it did not have mp4 codecs. It made the same complaint about avi and flv files.
That's mainly because they are non-free codecs so aren't included by default.
P.