In the jail, update all packages and install emby-server.
Package Options
Its reccomended to change some package options. Either build a package with poudriere with these changes, or make these changes on the emby jails packages.
FFMpeg
It's recommended to install ffmpeg from ports so that certain compile time options can be enabled.
Update the FreeBSD ports tree
Remove the default ffmpeg package
Reinstall FFMpeg from ports with lame option enabled
enable the lame option
enable the ass subtitles option
enable the opus subtitles option
enable the x265 subtitles option
Compile and install.
ImageMagick
It is recommended to recompile the graphics/ImageMagick package from ports with the following options .