Download ffmpeg - Roon will need access to the required codecs via the /Data/Codecs/ directory. You will need to download these codecs on another computer before placing them on ROCK.
For example, grab https://johnvansickle.com/ffmpeg/builds/ffmpeg-git-amd64-static.tar.xz and uncompress it. Remember, no additional files from that package are required, only ffmpeg.
If you are using Windows and do not have the ability to uncompress .tar files, we recommend downloading the open-source program 7-Zip