When a plug-in is currently selected in the plug-in editing window, clicking the “Output” tab button displays the following options:

The Read “output is ready” signal from popup menu lets you select one of the boolean outputs published by the Quartz composition. The value read from the selected output tells FxFactory when the plug-in's output is ready to be displayed, or whether the composition is still waiting for some assets to be loaded. While waiting for this output port to become true, FxFactory will continuously re-render the composition to give enough time to its patches to load and process the required assets. 
The Timeout after … seconds value lets you specify a maximum number of seconds that the plug-in will be given to load assets, before its assets are considered to be missing or unavailable (in which case, the render operation will fail). If the Warn user when assets fail to load option is on, FxFactory will notify the user when this error occurs. Timing Information.

The Feed output info structure to popup menu lets you select one of the structure inputs published by the Quartz composition. The value fed to the selected input is a dictionary which contains properties of the output image expected by the host: Image Info Structure.

When working on a Filter plug-in, the Match output frame size to popup menu gives you only one choice: “Source clip”. When working with a Transition plug-in, this popup menu lists two choices: “Source clip” and “Destination clip”. This option determines the size of the output frame generated by the plug-in when applied to a clip (Filter) or in between clips (Transition). Due to the current implementation details of Final Cut Pro and Final Cut Express, the size of the source and destination clips is always the same even in a multi-format timeline, and as such the choice you make for this option is currently unused.

The Add a margin to the output frame option lets the plug-in add an certain number of pixels around the input frame, and it is only available for filters running inside Motion or After Effects. The amount (in pixels) that you specify inside FxFactory will be customizable inside the host via a slider parameter if the Add a parameter to control the frame margin option is also turned on. Adding a margin to the frame may be useful when the effect renders pixels outside the original boundaries of the frame (for example, a glow filter).