Can I configure Flash to automatically disable xscreensaver while it's playing video? Or, conversely, configure xscreensaver not to trigger while Flash is playing video?
I've seen this question on disabling the screensaver manually.
You'll find different scripts in order to do that on ubuntu forum. It's quite hacky and it does not seem that a clean way exist.
I don't think you can do this in the settings for either flash or xscreensaver. However, is it possible that you are streaming video from another site? You could write a script that ran netstat and looked for established connections on a certain port or maybe site and then xset s off; xset -dpms ; sleep XXX, then reenable. Then just background the script.