Hi Matthew,
"...I must ensure that I will have some control as to what the thumbnail
will look like.
It's not much, but as a fellow stickler for thumbnail quality (inc. animated gifs) I sometimes run a manual ffmpeg/avconv command on a local machine then overwrite the thumbnail on the server via SSH.
It's also neat to build wiki pages akin to the following: http://openmeetings.org/wiki/OMwiki:Finding_aid
Sincerely, George