But, mlt can insert in two slice of video a 3d transitions? I have seen this project:http://gvfx.blogspot.com/
I know this project (created by anubis4d an Argentinian) . It is some FX filters that you can use with Open Movie Editor.
Hum how to explain that ?
All the transitions come from MlT and (it is a picture) we call them using it in Openshot.
FFmpeg is in the two cases the tool for the exportation not for the effects (here, like use it is Frei0r-plugins) and the transitions.

So you can not use it for create some transitions.