Correct workflow in Adobe Premiere for work with interlaced content

Question

I have in input a DNxHD 120 in mov container 25fps interlaced upper field, I have to do various kind of edits, cuts, replace some pieces with after effects compositions and at the end of all the job export everything as a MXF 25fps again interlaced upper field.

Until now I always worked only with progressive contents so I'm unsure if what I'm doing is correct:

• I imported the footage into the project

• Created a new sequence based on what i think is the correct format: 1080 25fps interlaced upper field

• Started cutting, pasting and replaced some after effects comps

• Export with media encoder using the DNxHD SD 1080i 50 (i wonder why i can't find a 1080i 25 preset), however even if is writtend 50 it seems i can pick 25 fps.

Is all this correct ? I mean what's the best practice ? I'm keeping everything interlaced upper field. I think Premiere is a professional software able to handle all the footage in interlaced without problems.

or

Should I instead convert and make everything progressive first and then export again back in interlaced? (i fear this solution is not very good)

I also have this error if i try to rotobrush the footage:

This is starting to confuse me even more, why i should use a 50fps ?

Answer 1

As for how to work... it all depends on what your final destination is. Are you working on a piece to be broadcasted, or for the Web? In the latter case, the final product should be progressive. If the former... the in turn it depends on your source material, which seems to be interlaced.

So you should:

1. Create an interlaced project, "1080i50". The "50", in this case, doesn't mean "frames per second", but "fields per second" (2 fields = 1 frame).
2. Work as you would normally in Premiere.
3. Export it in an interlaced format too. "1080i50" sounds good, but again, that depends on the final destination of your piece.