You can use 16-bit floating point OpenEXR clips in Action. You can use clips of different resolutions on separate media, but you cannot specify clips of different resolutions to act as the front and matte clip of a specific media. Here are some things to keep in mind when working with 16-bit floating point clips:

• When entering the Keyer from Action with a 16-bit floating point clip, the Modular Keyer opens, even if this is not set as the default keyer in the Action Setup menu.
• Action operations and settings that are supported with 16-bit floating point clips include 3d tracking, textures, displacement mapping, motion blur, blending modes, anti-aliasing, and depth of field.
• You can enable or disable colour clamping when working with 16-bit floating point clips in Action. The Colour Clamping button is located in the Setup menu’s Rendering section.
• You can set the output resolution for your Action composite to 16-bit fp in the Frame Depth box located in the Setup menu’s Resolution section.