Is it possible to reduce the sound quality while playing on line flash videos,such as youtube and such???

I've noticed that the sound is what eats most of the cpu cycles,and makes some youtube videos to stutter quite badly.

I want to belive that there is such a feature hidding somewhere on the device,such as to use a different codec etc

Nope. You can however try one of the Youtube apps available, if its Youtube specifically that is stuttering(it doesn't on mine, as long as you just watch it and don't scroll around etc.)