I've rebuilt my catalog of several hundred clips with three thumbnails for each clip. I get the option of using the midpoint thumbnail as the poster, but I'd like to use the end (or 3rd clip) for the poster. I know I can set this individually, but I was wondering if there is a way to do it for the whole catalog.
Choose the poster frame you want to use and set it under the thumbnails tab, you'll see a wee camera icon next to the right arrow.
Go to your edit menu and copy the poster frame, or Cmd C on a Mac. Then select the required clips you wish to paste the new poster frame to, and go up to the edit menu once again and choose paste thumbnails.
(Assuming you mean, paste the same poster frame to all clips)