Sound volume limit?

Hi! Is there a way to limit the sound volume in OSX?

I watch a lot of different kind of tv/net shows on YouTube, UStream and others. The only problem is that there are commercials, and generally the sound volume of the commercials is compressed, cranked up and maximised. Compared to the moderate, polite conversation in the actual show, the commercials feel like shouting through a megaphone. I don't mind the commercials themselves, just the volume.

For me to be alert all the time, ready to turn the volume down, feels rather stupid. Could it really be too hard to build an app or something in which I could say "the peaks you are getting now are the highest there can be, please lower the volume if the peaks suddenly get a lot higher" ?

I tried to play around with Audio Hijack limiter effects, but couldn't get it working - I'm not even sure if it's really possible. It was the only app I could think of.

I have tried to google an answer, but either it doesn't exist or I just can't find the right words.

Thanks in advance for any kind of ideas!