Chroma Key is an image effects technique for compositing multiple video streams on top of each by applying a hue based masked to the foreground images. Commonly a blue or green screen backdrop is used in film production for these purposes.
Within VDMX, using the 'Chroma Mask.fs' FX on a layer will create a color-based mask that is applied within the FX-chain. Pixels in the input that are within the tolerance range are set to become transparent through the usage of alpha channels.
As a source, you can either use pre-recorded movies or a live camera for doing pre-visualization on set.
Step 1: Add the 'Chroma Mask FX.fs' to the layer playing the blue / green screen footage to mask.
Adjust the 'keyColor' and 'range' values until the background appears black in the preview window.
Step 2: Set the 'Composition Mode' for the layer to the 'OpenGL- Over' option to prevent additive blending.
If using non-GL composition modes, use either the GLSL 'Mix' or CoreImage 'Source Atop-VV' option.