The Frame Rate feature allows you to choose the frame rate of the final video.
Free users can choose between 15 fps and 30fps.
Pro users can additional choose 60fps for smoother motion.
The lower the frame rate the smaller the file size but also the less-smooth the motion will be.
15fps = small file but jerky motion
30fps = medium file size and standard motion
60fps = largest file size with smoothest motion.