theaudiodb.com - They require a donation of $3 each month for proper access to the API. If someone becomes a sponsor to me on GitHub I can consider it.
MusicBrainz - We already use it for automatic tag fetching, CD metadata and album covers. This is what is used when looking up CD's you load.
MusicMoz - There isn't an API as far as I can tell.
gnudb - This is a cddb service, could possibly be integrated.
opencdindex - Same as gnudb
Gracenote - This is a paid service without an open API as far as I can tell.
musopen - There isn't an API as far as I can tell. This isn't a service for metadata, but for free music.

Yes, I already started the work of adding it, basically it's identical to what's in Clementine except that Smart Playlists will be in it's own tab instead of inside collection/library. The status on that is here: https://github.com/strawberrymusicplayer/strawberry/issues/264
However we are too few contributors so I'm not likely to complete it unless we get more contributors to the project.

My usual way to listen to music is shuffle the least recently played. Would be handy to at least sort by date last played.
[sorry for the separate posts but site wouldn't let you edit except for shortly after you post]

@rustyleerhoton said in Fedora-FDK-AAC:

FDK-AAC

You need to ask Fedora.

FDK-AAC is part of GStreamer Bad Plugins:
https://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-bad/html/gst-plugins-bad-plugins-plugin-fdkaac.html

On Linux this depends on what file manager is in use. I recently added some extra code so that nautilus and dolphin works with selecting file, while others like thunar does not, because it does not have support for selecting files.

https://github.com/strawberrymusicplayer/strawberry/blob/master/src/core/utilities.cpp#L335