I cannot begin to tell you how many times I have had this problem. I have several church clients who all want "the outdoors" on their screen "indoors" (go figure).

Bottom line is they all tend to use camera footage which is interlaced. In addition to that, I also get tons of IMAG feeds which are also interlaced.

It's a nightmare

Here is the solution. Don't tell the content creator anything about the output file or the or the aspect ratio. Instead, have them export their files as close to uncompressed as possible in either a standard 3:4 size or a 9:16 size.

Just give them the crop specifications to create a window proportionate to the output screen.

What I mean by this is for example if you have 3 1024x768 projectors doing an edge blend of 25%, you'll end up with 2048x768. If you do the math, a scale conversion of that is 1920x720. This means that you tell your content creator to make an HD file at 1080p but you tell him the window frame is 1920x720 and the top and bottom strips 180 pixels are just dead space.

Once he outputs the file and sends it to you, you do the conversion, crop the file, and render it in the correct codec using one of the nicer programs like Richard mentioned for doing your interlaced to progressive conversions.

Incidentally, there is another thread that talks about i vs p and I would recommend you read it because there is a website link in there that shows just what kind of problems you'll run into converting from interlaced to progressive.