Record "black" frames

Hi,

I need to create a 5 seconds FLV file that doesn't have content, only black frames.

I've trying with something like this on the server side (onUnpublish):

application.onUnpublish = function(p_c, p_stream)
{
     serverStream = Stream.get('emptyVideo');
     serverStream.record('append');
     serverStream.play(p_stream.name); 
}

any ideas?