We understand your pain, it's a problem that should be more easily explained and dealt with at the operation level. Users really shouldn't be expected to knwo all this stuff or to find it out the hard way.
Interlacing can be introduced anywhere along the production pathway. How and when to eliminate interlacing is a difficult decision to make competently until you have immersed yourself in video for many months. There are no easy solutions. We all learn about controlling our interlacing by failing.
You start with your final output requirements and work backwards. If your output requires fields, you must work with formats that support fields and interlacing and maybe you'll need motion blur.
To understand how interlacing works, you must view your output on a field-capable display by hooking up a video monitor to your computer or learning how to set your Mac's display to show you interlaced fields on a progressive display. Your graphics card, drivers, and Mac specs determine if that's even possible, can't help you on those variables.
Video is very hard.
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