Some applications can load Vuo compositions as plugins — making it possible for you to customize or add to the application’s behavior. For example, CoGe and VDMX, VJ applications that do media mixing and compositing, let you mix in visual effects made with Vuo. In order for a Vuo composition to communicate with CoGe, VDMX, or another application, you need to create the composition in a special way using published ports and protocols.
In Quartz Composer, there's a single, default rendering output. VJ apps typically capture that output and mix it into the VJ app's other feeds, so there is no need for a protocol for composition playback. In Vuo, use the Image Filter or Image Generator protocol to produce output.
If you’re going to use a Vuo composition in an application, usually the application expects the composition to have certain published input and output ports. For example, an application that supports Vuo compositions for video effects would expect the composition to have a published input port that receives an image and a published output port that sends an altered image. To guarantee that your composition’s published ports match what the application is expecting, you can use a protocol. The composition shown above adheres to a Vuo protocol.