if you bring in a footage type that ae thinks is commonly interlaced (like dv), then it interpret it as interlaced and try to separate the fields. then by default, ae renders progressive, so it will often de-interlace your video. if you don’t want this to happen, there are ways to handle this…
if you select the footage in the project window, at the top of the project window you’ll see the thumbnail and some info on the footage. one bit of info is often the field interpretation (like, separating (even)). this means that ae is separating the fields, even lines first. if you don’t want that (or maybe ae is wrong), select the footage and choose file>interpret footage>main. here you can define how you want the footage to be interpreted.
most of the time you will want ae to separate fields if the footage is interlaced, however, you may want to put the fields back when you render.
if you want a field render, when you add the comp to the render queue, click the render settings and set field render to the correct dominance. now when you render the comp, it will interlace the render (both for the footage and any motion graphics/effects you’ve added). note that the render will usually take twice as long as ae is rendering and doing calculations at 60 fields per second vs. 30 frames per second.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW