Jur4nd
(Jur4nd)
3
I think that for high Quality Videos you should use DUMPMOVIE and BENCHMARK parameters, that way it will perfectly EPIC! 
more details can be found here:
https://docs.unrealengine.com/latest/INT/Programming/Basics/CommandLineArguments/index.html#rendering
I would also recommend to take a look on similar post regarding to UDK like this one: