Here is a hack where you have to do very little actually, its mostly about the discovery. When using Firefox on GNU/Linux, the Adobe Flash plug-in automatically downloads flash videos you are viewing in Firefox to your /tmp directory.
e.g. when I view http://www.youtube.com/watch?v=xO0gSJGJ7Fs in Firefox, a randomly named file /tmp/Flashn3T33b shows up, which I can play using mplayer, copy, rename, do anything with. When I close the tab, this file is deleted, but the plug-in does forget to clean up on few occasions.