Convert 100fps, 1/100s footage to 25fps, 1/50s footage

[Mei Lewis]

Not sure where to post this question, hoping it fits in the VFX forum.

 

I'm trying to work out how to convert 100fps, 1/100s footage to 25fps, 1/50s footage inside Premiere, but I'd be willing to try other software.

 

I should be able to do it like this:

If the frames are numbered 1,2,3,4,1,2,3,4,1,2,3,4,.... and so on then I need to take frames 1 & 2, average them and combine into a single frame, then ignore frames 3 and 4 and so on. So every four frames of input generate a single frame of output, with effectively twice the shutter time, which is what I want.

 

My first step towards this was to make sequence inside premiere at 100fps where the digits 1,2,3,4... appear each for one frame. This would allow me to very clearly test any method for converting 100fps->25fps.
 

I've made this as a sequence, now I need to get it out of premiere into a video file, so I can then re-import it and test. BUT premiere refuses to export anything about 60fps. I've searched online and in several places Adobe says this is because professionals don't want anything about 60fps - which is so wrong it's silly.

Anyway, does anyone know a workaround?

Or does anyone know how to do the conversion I'm after directly, without making this intermediate test file?

 

Thanks!