a little hacking and wiresharking later, one can use
http://camendesign.com/code/video_for_everybody/test.html
to download videos with range request from the files store and play them in the browser.
(download the html file, edit it, enter the room in another window, load the file from disk -> video plays and is fastforwardeable)
lets see whether this is able to work with attachments too, and how one could have transparent decrompression too.
