I have tried this:
kid3-cli -c "filter '%{album} equals \"\" and %f contains mp3'" -c "set album '(unknown album)'"
This sort of works but has some problems:
- Although it filters out the non-mp3 files, it seems not to do short circuit evaluation. For instance, I have a zero length (bad) .mp4 file. When it reaches this file it gives me a ReadChildAtoms error. Apparently it tries to check the album (failing to do so on the zero length file) before it checks to see if the name contains .mp3 (and changing the order doesn't work either).
- It doesn't limit itself to the current directory.