I've been trying some things. The only thing that seems to work is just putting a plain link to the file. The bulletin board does not recognize it as a video and does not display it, but clicking on the link works. I think this means that opening the link in the browser works and the bb really has nothing to do it. Here are two such links. The first is from my Google Drive, the second is from YouTube.
https://drive.google.com/open?id=1V5fWA ... 0RXKMjb9DIhttps://youtu.be/fx7fKIHMAjQI found a few references to this problem in the help areas for the phpBB. One thing I saw suggested that it's possible to upload a video using same "upload attachment" feature we use for photos, but there is a file size limit (probably set to 1M, too small for video) and also a list of legal file extensions. It may also require some extensions to the base phpBB software. Accepting video uploads is a whole 'nother range of commitment for the hosting site, and I quite understand not going there. The discussion is here:
https://www.phpbb.com/community/viewtop ... &t=2386721.