Currently using Hardy, some flash files (.flv) do not have thumbnails in nautilus. Also, those files that fail to thumbnail take a long period of time before they are skipped. This is a regression, as in previous versions of Ubuntu these same files would have thumbnails in nautilus.
I don't think there is anything special about the files in general, they _are_ flv's saved from youtube.
I can provide this if its of any use:
matthew@matthew-desktop:~$ gst-launch-0.10 -t filesrc location=/media/hdb5/My\ Videos/YouTube/Nirvana\ -\ basement\ jam.flv ! decodebin ! fakesink
Setting pipeline to PAUSED ...
Pipeline is PREROLLING ...
FOUND TAG : found by element "ffdemux_flv0".
video codec: FLV video
FOUND TAG : found by element "ffdemux_flv0".
audio codec: MPEG-1 layer 3 audio
Pipeline is PREROLLED ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock
FOUND TAG : found by element "mad0".
layer: 3
mode: mono
emphasis: none
bitrate: 8000
Got EOS from element "pipeline0".
Execution ended after 7024614009 ns.
Setting pipeline to PAUSED ...
Setting pipeline to READY ...
Setting pipeline to NULL ...
FREEING pipeline ...
If a copy of a flv is required to find the cause i would be happy to upload one.
Thank you for your bug. That's not likely a nautilus issue since it doesn't do the thumbnailing but just call whatever software is registering those, could you attach an example to the bug?