pre_install() {
  cat <<'EOF'
NOTE: mpv has several optional features that are automatically enabled if the
required libraries are present at configure time. This package does not include
any of the optional features as dependencies by default (but it does add depends
for whatever is linked against when building the package). If you want to use
any optional features that require libraries you don't currently have installed,
please install the relevant libraries and rebuild the package. A frequently
desired optional feature is Lua support, which is necessary for the on-screen
controller "GUI", youtube-dl integration, and other extension scripts. Lua
support can be provided by lua52 or luajit.
EOF
}