<p>I got this flash application where you can click a link while watching a video. It will open a new tab and pause the video. Now when you come back to the flash application it would be nice if the video would start playing again. Is there a way, an event or so to do this ?</p>

Flash is probably a no-go, but you might have some luck with pure javascript and have that communicate with your Flash Movie. I suggest you play around with the Window's onFocus event.
I've never used it before, so it might not trigger on any/all browsers.
This
worked in FF3. It's not valid or good code but it's a stepping stone for you:
```
```
<html>
    <head></head>
    <body onFocus="alert('testing');"></body>
</html>
```
```
It's also really annoying because clicking okay ok the alert, re-triggers the focus. Control+W will close the tab for you and allow you to break the cycle.