Hey James,
So after talking with one of Cinematics Team leads the process that they use is all the tools inside UE4.
He walked through the creation process by creating a matinee. When it was time to render out the images the All the options were checked in the window form Cinematic Mode down.
It was suggested that you may want to enable the “Close the editor when the capture starts” option as well.
Once these images were rendered, or even the video, they are brought into Adobe Premiere and from there the sound, titles, and all the bells and whistles are added.
This is Epics process. The Command Line Arguments are no longer used internally.
Speaking with another dev regarding the command line arguments -BENCHMARK and -FPS are not supposed to work with a packaged project in this way. There is a feature request in for -DUMPMOVIE to be enabled for non-packaged projects (UE-4879), however this is marked as “Trivial”. Feature requests are not guaranteed to make it in the engine.