We needed to incorporate an openframeworks application in a Max / Jitter patch for a performance my friend was doing, and we found an incredible open source application called Syphon (syphon.v002.info/) which allows applications to "broadcast" to each other via a Server / Client relationship. The feed is taken directly from the graphics card with openGL rather than "capturing" the screen, so you can get a pretty great framerate. You can even composite the captured footage in Max with other effects (or vice versa). Here's a brief walkthrough of the workflow.

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