On Gentoo mpv_identify.sh is only installed by media-video/mpv[tools], so
naming the bare package sends the user to a build that still lacks the helper.
Carried over from app-misc/mc's mc-4.8.29-gentoo-tools.patch.

--- a/misc/ext.d/video.sh
+++ b/misc/ext.d/video.sh
@@ -21,7 +21,7 @@
         elif command -v mpv_identify.sh >/dev/null 2>&1; then
             mpv_identify.sh "${MC_EXT_FILENAME}"
         else
-            echo "Please install either mplayer or mpv to get information for this file"
+            echo "Please install either mplayer or mpv[tools] to get information for this file"
         fi
         ;;
     esac