Is it normal that Audio Airplay doesn't sync with Video?

When I first heard Mountain Lion will be able to airplay all my system sounds to my Airport Express I got really excited.

Now that I bought ML and configured everything I'm very disapointed...

Safari does not sync Audio and Video... neither does VLC-Player...

I'm not able to watch a YouTube Video without a 2s audio delay...

Am I doing something wrong or did Apple sell me something that doesn't work properly?

Thanks

ExWoW