Custom FFmpeg Export Options

'Peter 12Aug15: ToDo-1 As far as I can see this has never been documented.

The Custom FFmpeg format options dialog appears in response to the Open custom FFmpeg format options button in the Export Audio or Export Multiple dialog Options pane when you have chosen Custom FFmpeg Export in the Save as type dropdown.

Peter 12Aug15: I'm pretty stuck as how to proceed further with this - it's way beyond my envelope of knowledge and experience ...