To save a lot of OSF bandwidth and to speed up the loading of content, I would strongly suggest the use of the poster=path/to/poster.png and preload="none" attributes of HTML video nodes. This would impact the video preview panel when browsing project files and also videos embedded in the wiki using the @[osf](GUID) method.

It would also be nice if eventually the poster images could be selected by the users when uploading video files, but I would say this is lower priority for now. At a glance, perhaps this could be achieved using export handler that generates a thumbnail at a user specified offset.