Yeah, sorry, I thought it best to not leave anything out, just in case.
There is another way to go though. Since system 10.3, maybe earlier,
QuickTime performance improved a lot, possibly because of Quartz
Extreme. You can play two full frame rate movies with transparency
changing in Director, with them set to be non direct to stage, and get
away with it.
This is what I've ended up going with: two qt movies playing one atop
the other with director doing the transparency between them. The
alternative of using a Director text member would be fine if I knew
more about Director and felt more comfortable poking about in our
existing project without fear of breaking everything. There's also a
rather irritating domain specific problem; our text is Unicode heavy
and Director has no Unicode support... but that's a problem for another
day and another mailing-list I think ;)
Thanks for the pointers tho', Much appreciated as you've saved me a
world of stress!