Client asked me to track Prezi in Google Analytics. However, there is no way how to track iframe embed. Thus I had to use Prezi API to make this running. API is only alfa right now but I hope this basic function will work for a long time. I used Google Tag Manager to make this running.
Update 2018: After Prezi API update, this solution does not work properly. Feel free to fix it and send us updates. We will give you credits.
Find more at MichalBlazek.cz or try demo