The file you have mentioned is available as part of the FFMPEG library, usually also included when you install VLC.
You can download the FFMPEG files from the following link: https://ffmpeg.org/download.html that should resolve the error.
I hope this is helpful and if you have any other questions please let us know.
the plugin is not working so I looked into what I could find
I noticed that these library files are not on my MAC and where not in the download
how do I get these files (are these missing files my problem)