FFMPEG problem - no suitable decoder found

This is on Windows 7 with Retroarch 1.8.5 but probably started way earlier because I had "fixed"the problem before by copying my RA Config from 1.7.7 into the folder of a nightly around 1.8.2. But since it persists I decided to look further.

Retroarch can’t launch any videos, the log telling me that there is no suitable decoder and Codec

[libretro ERROR] Couldn’t find suitable decoder, exiting … [libretro ERROR] [FFmpeg]: Failed to find codec.

Copying the old config into the 1.8.5. RA folder solves this, so I looked into the generated config of 1.8.5 in my user folder. I can’t see any noteable video differences there though, so what could it be? Directory related?