Export 12 fps

I would like to take a video and export it as a png sequence at 12 fps or better yet 8fps. How do I do this? This would mean a 10 second clip would render out 120 frames (or 80). I know how to render out a png image sequence but is there a way to control the frame rate?

I'm working on a mutlie media stop-motion piece. I will print these images, cut them out and animate them using a stop-motion process.

Thanks.