media-video/ffmpegthumbnailer don' t work on xfce4.8.0

[ev56o]

When i open the directory with thunar i see the icons of the image files with non thumbnail.
If i open an image file with gqview the thumbnail is generated and i see it on thunar as thumbnail normaly.
I use profile amd64-nomultilib everything is up to date
USE="python remote a52 dv dvb mpeg theora xv 3dnow kde qt3support consolekit xmlwriter xmlreader sockets soap pdo mysqli mysql mysqlnd imap cgi sysvipc sqlite3 dhcp dvd fbcon libv4l2 val2 ogg twolame opengl gnutls gd fat ntfs reiser4 reiserfs xfs ext4 lcms webkit pdf aalib tools png cjk openxml xvid ffmpeg wavpack vorbis mp3 lame fluidsynth cdda aac cairo php apache2 qt4 jbig sqlite extras xml policykit device-mapper gdu gstreamer alsa fuse nsplugin svg jpeg jpeg2k tiff java alsa dbus libnotify startup-notification xfce_plugins_trash gtk quicktime -ipv6 udev xorg X mmx sse sse2

[ev56o]

Can i have some help?
I tried to enable more flag use for ffmpeg and it doesn' t work.
I tried tumbler with xfce and thumbnail work for image only but this isn' t the right way. It must work with ffmpegthumbnailer only.