Added videoInArchive and videoInMediaFolder elements to schema (actually started with only video element but that proved inadequate),
added code in transform.xsl to transform that into a video element,
got Pat to provide preferred css for the video element and
put the video data file in the appropriate folder.
Now have working video element, for example in the ParksCanada video page in the archive. Still have to create an ogg version of the data file.