Ahoj,
I suggest to add 'libavisynth.so' to the 'provides'-array.
Reason:
* There are many packages in the AUR which depend on 'libavisynth.so',
* the AUR-package 'avisynth-git' also provides 'libavisynth.so',
* 'avisynthplus' installs '/usr/lib/libavisynth.so*'-files.
Regards!
Additional info:
* package version(s): 3.7.2-1