Sun Aug 04, 2013 9:50 pm
Ok, i wasn't quite thorough in my answer...
All BluRay players must support three standard formats: 1080@24p, 720@50p and 720@60p. Some player support different size/fps combinations as well, especially newer ones and software players; but to stay fully standards compliant your video either has to be 24 fps at full 1080 or 50/60 fps at 1280x720.
Most "export" functions in editing applications only let you choose these formats, so i assume your application wants to create 1080@24. If you put 60i material on your timeline, the application has to convert the framerate somehow, and there are several ways: Usually the 60i fields are first de-interlaced into 60p frames. Then the simplest way to get 24 fps is to only use 24 out of the 60 frames and drop the rest. But because 24 is no integral divisor of 60 you can't just take every 2nd (that would result in 30 fps), sometimes you have to skip more than one image, that's why simple "frame dropping" results in stuttering pans. Better algorithms create additional images in between the recorded images, either by simple blending, or by motion compensated interpolation. In both ways the software has to invent new images, and that will always go wrong occasionally...