Okay, I've managed to get this working by adding a couple of appropriate plugins. However, the thumbnails for all of the mp4 files are identical. I'm perfectly happy with the graphic being identical, but each graphic has a bottom line that says simply ".mp4a". I've got the mouseover effect working so the title of the recording can be seen in that way, but is there a way to have the appropriate text label (say the filename) displayed on or below the thumbnail. I'm thinking maybe not without a lot of work. But worth asking.
Thanks.