(I'm still very much a newbie.) When I export my chroma-key video from AE, it looks like the attached AE-black.png (black background) and/or AE-transparent.png (see the attached screenshots). No green fringe. I export using MOV/Apple 4444 because I want both RGB and alpha. But when I import the video into Premiere, my video has a green fringe that I don't see in AE. (See premiere.png)
Are you definitely exporting an alpha channel? Put a layer behind the footage in Premiere to check.
Are you rendering your file color as "Premultiplied (matted)" or "Straight (unmatted)"? 7 times out of 10 I'd render Straight, but if you're compositing onto black or very dark backgrounds you may prefer the look of Premultiplied.
Make sure your output settings look like this:
If these settings still don't solve the problem, you need to use a Choke effect (either within your keyer like Keylight, or apply one of the standalone Choke filters, to trim a few extra pixels from the edge of your key.
I'm positive I selected RGB + Alpha (and verified with static image behind the chroma-keyed clip).
> ...file color as "Premultiplied (matted)" or "Straight (unmatted)
I'm going to have to look up what this means.
I'm not seeing anything I need to choke in AE. And in Premiere (where the problem manifests itself) I couldn't find a 'choke' effect per se, but I applied UltraKey, made the transparency my key color (?), and the choke setting worked like a charm.
I still don't understand why what my clip looks like when I render it in AE looks so very different when I import it into Premiere. But 'choke' solved my immediate problem. Thanks so much!