I made a small change to Whaat's code so it pads the filenumbers with leading zeroes, I hope you don't mind.

Just change this line (line 107):

@image_path=File.join(@export_path,@filename+"#{@frame}"+".#{@format.downcase}")

to this:

@image_path=File.join(@export_path,@filename+"#{@frame.to_s.rjust(10, '0')}"+".#{@format.downcase}")

Thanks for the plugin Whaat! Best regards.

A very slightly modified version of Whaat's Smoothstep Animation script that pads the output filenames with zeroes for better sorting.