Altering RTMP stream for other services.

I built a Nginx server on Digital Ocean to stream to multiple streaming services. Here is my current configuration :

http://pastebin.com/GMYY4Mc7

I'm trying to use FFMPeg to transform the stream to stream to Facebook and Periscope but they have different requirements for injection. They require a lower framerate, screen size, etc. Any suggestions on how I can use FFMPeg to convert and restream to those endpoints?

Thanks.