Then I try to watch TechTalk with Rhythmbox and no chance to do it.
After reading many forums, and many try, on it I realize that is a Gstream bug (officialy granted).
So I decide to install Totem reader and ...

Godd audio but poor video. It's so unfocused that I guess presentation's text.
Is this a choice to reduce bandwidth?
By the way, I looked at WMV file!