Well there's a program for Macs called Screeniks which automatically takes a bunch of screenshots at even points from beginning to end of the clip. You can certainly drag a folder or all files in a folder into the Screeniks window and have them generate all at once. Of course the screens will only be at whatever number of caps you tell it to take, at mathematical intervals rather than some carefully selected "perfect moment" for each one. But theoretically if you set it to take enough caps from each file, it will be able to capture enough to give a good example.
I made this screencap with it:
http://www.facialforum.net/attachmen...8&d=1259447215