Masking out the video background in Sony Vegas I have a video and I need to mask out the background for it.


A screenshot from the original video, credits to The Muppets Studio

The video has been shot with a still camera on a steady background. 
My goal is to mask out the background (e.g., everything not related to moving objects).
I don't have the original sources, of course.
It is also hard to recreate the background (I mean, to precisely match colors).

My approach, in theory, is the following:


Collect a series of screenshots where different parts of background are visible (when objects move away);
Glue those parts into a background image (see image below for a partial result);
Place the background into a layer and compute the color difference between the original video and the background;
Build a set of pixels for which:


the difference is nearly zero (within a certain color threshold occurring due to rounding/compression problems);
and within a certain minimal area (so that individual pixels did not occasionally appear);

Wrap those pixels into a key mask.


Still, I'm stuck with building a proper structure of layers within Sony Vegas to accomplish my goal.

How this can be done?


My backround attempt

My environment is:


Sony Vegas 12.0/x64, I'm not considering another software;
Basic set of plugins/filters, but I will also appreciate references to 3rd-party plugins, even the commercial ones;
Still, I would prefer a "clean" approach based on masking.


Thanks a lot!
chroma key choose a colour*drag) then take eye dropper and select background in the preview window