FileBot

I am trying to shrink my library and have filebot call ffmpeg to transcode videos to x265 *before* moving to the new directory.

Digging through the amc script on github looks like the file is already renamed & moved before '-exec' is applied.

Is there an option I am missing that might help do what I'm trying to get done?

The easiest way is probably to process files to a local output folder, and then transcode & sync to the final output folder via -exec or --def exec.

You could also, literally, transcode all your files with ffmpeg before calling FileBot, and then just call FileBot on the transcoded files afterwards.