Grass Valley Maestro Master Control v.2.4.0 - Manual (Page 248)

MAESTRO User Manual 244
Upstream Keyer Operation
Adding One Key to Another (No Background Change)
Assuming that one keyer is already on Program; select both keys on Preset.
Perform a transition.
The same technique can be used to add up to the maximum number of key
layers (four).
To remove a key, make sure the Preset button for the key is OFF; then
perform a transition.
Changing Background Without Changing Key
To hold a key on Program, select the key’s Preset button. A transition to a
new source can now be made without changing the on-air the keys.
Note Upstream keys are unaffected (held on Program with no visual change to the
key) by background changes only if the selected transition type is cross-fade
or cut. The transition types fade-cut, cut-fade and fade-fade will take the key
to black with the background video before re-displaying it on Program
To take out the key, de-select the Preset button and perform a transition.