When using tumbler with the thunar file manager to generate thumbnails,
tumblerd fails and just leaves empty files in /tmp. Inspecting the log with
dbus-monitor --session --monitor
interface=org.freedesktop.thumbnails.Thumbnailer1
yields "No thumbnailer available for "file:///foo/bar/baz.mkv"", in this
case for mkv files. Making ffmpegthumbnailer available to tumbler
apparently fixes this. I'm not entirely sure if it should be made a hard
dependency, because in theory users can freely pick the backends and at
a later time others might become available.
I stumbled upon https://issues.guix.gnu.org/37276 where gstreamer has
been removed and I don't understand why it's been done. The message only
mentions "https://issues.guix.gnu.org/37276";, but as I understand it
gstreamer was very much necessary because without an appropriate backend
tumbler won't show thumbnails...
