[Nigel Phillips] "I use Sony Pro11! I have some Pre Keyed Footage, some with black and some with grey background. How can I make the back ground transparent?"
You want to use a Luma Key but Vegas Pro doesn't have one (Boris Continuum Complete does but I assume you want to do this in Vegas alone). You can achieve the same thing in Vegas but you need to make your own mask. Here's how:
What you need to do is create a mask from the footage and then apply that back to the footage using the Multiply (Mask) compositing mode:
(1) Duplicate the footage on a track above
(2) Add the
Sony Mask Generator to the footage on the top track.
(3) Adjust the
High In parameter until you see a complete Black & White mask
(4) Change the
Compositing Mode of this top track to
Multiply (Mask)
(5) Press
Make Compositing Child in the track header of the original track below
The black should now be transparent and show the track below. Like this:
~jr
http://www.johnrofrano.com
http://www.vasst.com 
