No subject

or upon the Work and other pre-existing works, (...) or any other form
in which the Work may be recast, transformed, or adapted, except that
a work that constitutes a Collective Work will not be considered a
Derivative Work for the purpose of this License. For the avoidance of
doubt, where the Work is a musical composition or sound recording, the
synchronization of the Work in timed-relation with a moving image
("synching") will be considered a Derivative Work for the purpose of
this License."


When Creative Commons adopted the position that cc-by-sa covered
images do not enjoy the same protection as sound in situations where
it is synchronized with sound or text it was shocking and upsetting to
a number of people.

So while it's the whole weak/strong copyleft issue needs to be fleshed
out, I don't think it's fair to just state that cc-by-sa is currently
a weak copyleft, even if that is the intention of the licenses'
stewards with respect to visual works.