The BitmapData.draw method in Flash, is protected. If you try to write a MovieClip from another domain/website into a BitmapData, you will get a SecurityError. Unless this domain authorizes other domains with a crossdomain.xml policy.
I learned this when trying to write a Youtube video on a BitmapData.
Youtube is not cool, but fortunately, Vimeo is! Yes, Vimeo authorizes all of us to write their videos on a BitmapData, allowing a bunch of fun experiments (http://asciimeo.com/).
All you have to do is request the right crossdomain.xml, which is not documented on their site (http://vimeo.com/api/docs/moogaloop) .
I knew that asciimeo.com was using BitmapData.draw on Vimeo videos, so all I had to to do is open a video on asciimeo, and use firebug (http://getfirebug.vom/) to capture the crossdomain.xml urls. And it worked!
Here are a bunch of calls you have to add in your AS3 projects to allow Vimeo videos being written on BitmapData :
Tanks to http://twitter.com/peter_nitsch and http://twitter.com/UnitZeroOne who pointed me to Vimeo.
As I already told, Vimeo is a cool community, visit their forums where you can reach the staff : http://vimeo.com/forums