When opening a folder with Ogg/Vorbis files in Nautilus, syslog logs many
errors of the type:

org.gnome.Nautilus[3359]: (nautilus:25991): GnomeDesktop-WARNING **: Error
creating thumbnail for file:///home/user/z.ogg: Unrecognized image file format

Obviously Ogg/Vorbis is not an image format. What's broken here?

Looking for similar errors in the past I found these:
(.odt)
org.gnome.Nautilus[4054]: (nautilus:4656): GnomeDesktop-WARNING **: Unable to
create loader for mime type application/vnd.oasis.opendocument.text:
Unrecognized image file format
(.sxw)
org.gnome.Nautilus[2173]: (nautilus:2540): GnomeDesktop-WARNING **: Unable to
create loader for mime type application/vnd.sun.xml.writer: Unrecognized image
file format
(.ac3)
org.gnome.Nautilus[2140]: (nautilus:2473): GnomeDesktop-WARNING **: Unable to
create loader for mime type audio/ac3: Unrecognized image file format
(.flac)
org.gnome.Nautilus[2140]: (nautilus:2473): GnomeDesktop-WARNING **: Unable to
create loader for mime type audio/flac: Unrecognized image file format
(.mp3)
org.gnome.Nautilus[2140]: (nautilus:2473): GnomeDesktop-WARNING **: Unable to
create loader for mime type audio/mpeg: Unrecognized image file format
(.wav)
org.gnome.Nautilus[2147]: (nautilus:2712): GnomeDesktop-WARNING **: Unable to
create loader for mime type audio/x-wav: Unrecognized image file format
(.ogg)
org.gnome.Nautilus[2147]: (nautilus:2712): GnomeDesktop-WARNING **: Unable to
create loader for mime type audio/x-vorbis+ogg: Unrecognized image file format

(More unknown extensions are .docx, .html, .pdf, .ps, etc.)