You can create chroma keys directly on the timeline using the Axis Keyer. When you enter the Axis Keyer, the clip loaded as the Front is the clip with the Axis soft effect, and the clip loaded as the Back is the next available layer on the timeline.
The Front clip is provided by the clip with the Axis soft effect.
Image courtesy of Behavior Communications Inc.
The Back is provided from the next available clip in the multilayer timeline
Image courtesy of Behavior Communications Inc.