not smooth dvb image

 >> If you look *very* carefully at the face of the man speaking, you
 >> can see what I mean. (especially around the eyes).
 >>
 >> Thanks
 >>

 >it's definitely interlacing, although I can't see each line 0.5 cm
 >think :)
 >Other variations of yadif may improve the quality even more
 >(read the man page)

I've found an example where the effect is much stronger.
Look at the file (5MB) it is the beginning of Star Wars, from ITV1
If you look at the text scrolling up, you'll see a very strong effect of "lines", like 
"discontinuity in the text"...

http://xoomer.alice.it/enodetti/log/lines.avi

I've tried a few filter, like the one you suggested and I could not get any better result.
Someone said it is quantisation artifacts rather than interlacing.

Any idea how to get rid of it?

Cheers