gst-thumbnail issue

Hi all,

Nautilus uses gst-thumbnail to generate icons for movie files. It happens
sometime that gst-thumbnail selects a black or almost black frame from the
movie, and this looks ugly. My first question is how does gst-thumbnail
selects a frame from the movie ? It just take a random shot ? I guess not,
because it gives always the same output.
Another question is if this behavior can be modified, for instance we can
select to re-thumbnail a file if the first thumbnail was not acceptable,
or even we can make it recognize bad frames, and seek further.

Thanks,