My mistake – when I wrote “export” I meant ctrl +m and the whole journey through Render queue. I’ll be more precise in the future.
After six hours of fighting with keyligh i’ve found out, that’s not keylights fault. It’s a matter of dv footage i received. It has some noise [or grain] on it and after keying it’s just sligtly more visible, than before keying. I’ve learned a lot during these 6 hrs, but my video still looks noisy – so now the question is – is it possible go get grain-free dv footage? Id not – how to reduce this graininess.