chroma keying tutorial etc - for "one zoom" masking of white

In order to project the onezoom.org video on the dome, without all the white background dazzling viewers, looked for ways to convert the white background to black background.

Chromakeyer tutorial - https://www.youtube.com/watch?v=dI1kMT3O6uk

But we might not be able to use that? Maybe if we make the clip green?

Green screen tutorial - Ryan King Art

https://www.youtube.com/watch?v=KBBkgoDPnZE

Finally ended up using inverted Y images (video) as mask, then increased contrast 3x with Multiply 3x.