Rendering to create an interlaced file from AE

Question

in After Effects 10.0.2.4
AE timeline > Composition Settings > Frame Rate: 29.97
in the render Queue,
Render Settings > Field Render > "Upper Field First"
but the file comes out
Progressive.
.mov, mp4, m2v ... all progressive.
our Chyron Mosaic Clip player says "this file from AE is progressive. i won't play it. i want interlaced."
also, a MediaInfo says "yep, it's progressive."
what is needed to be done to render this so the final file is interlaced?
thanks in advance for any help you can give
al b

Answer 1

Here's the deal. If you have progressive footage at any frame rate and you separate fields then you have two identical fields. In AE you don't have holes in the scan lines like you do with NTSC footage because the holes are filled in by interpolation so the combing effect is minimized, and if you separate fields the empty spaces are filled in by interpretation. There is no description of the footage you used in your project in this thread so I can only assume that your project contains only progressive original footage and that the other elements in the project are not moving. Here's why:
If you put progressive footage into the Render Cue or the AME and you select separate fields, the time difference between fields does not exist so when the footage rendered as interlaced so you will end up with pairs of identical fields. There's no way around that without doing some fancy time manipulation in the composition timeline. (Twixtor, Time Remapping, Frame Blending). If you want to have double the time slices, like you get with interlaced footage, then you have to use some temporal processing to create those in-between slices of time.
I just checked this out with CC using both the render cue and the AME. There is absolutely no way that I can take a project that has moving elements and not end up with interlaced footage where each field is a different moment in time. There is also no way to create unique fields from progressive original footage without some kind of temporal processing in the timeline of an AE comp.
Here's how to check for interlacing:
Import your file into AE
Check file interpretation by selecting the footage in the Project Panel and then go to File>Interpret Footage>Main
Turn on Separate fields
With the footage still selected go to File>New Comp from Selection
Go to the Composition settings, select the frame rate, use the right arrow key to move to the end and type in *2 to double the frame rate of the composition
Step through the project one frame at a time using the Page Down key or Cmnd/Ctrl + right arrow key and check for motion in the frame
Go back to file interpretation and reverse the field order
Repeat step 6
If the motion is all in one direction in step 6 but goes back and forth in step 8 (or vice versa) then your footage is interlaced and the problem is with the metadata in the footage. If the footage shows two identical frames at a time then even if it is interlaced, it will appear as if it is progressive because you have identical pairs of fields.
If you still can't make this work then take a clip that will work in your Chyron Mosaic Clip player and analyze it. See where you can find differences. Recompress the clip using the AME or the Render Cue and see if that works.