Here is what I want to do: hook up a keyboard shortcut with an action to play/pause the video that is currently open in a Google Chrome tab. Would it be possible on Mac OS X?
I was thinking about keeping Youtube always in a particular tab (e.g. the first one) and creating Automator script with a keyboard shortcut. I know it would be possible by simulating user actions (switch to particular tab, simulate click, go back to last tab) but I'm looking for more smooth way.