I want to make a 720p60fps Video, but when I change it from 30fps to 60, it shortens the video. Why is that?
If 1 second amounts to 30 frames in your video that makes it 30 frames a second, although your timeline is now set to 60fps your video is still 30fps, hitfilm is compensating for the extra frame(squeezing it down to fit the framerate of the timeline) - hence speeding it up, if it didn't do this the video would jump or stutter due to the frame duplicate (frames 11-22-33-44-55-66 and so on) to keep the 30fps video within the same time on a 60fps timeline.
Yeah, is to do with how the frames in the video are mapped onto the timeline. Set your project settings to 60fps, if that's what you want, then make sure your video is set to 30 fps in its properties, then add the video to the timeline. If it asks you to change the project settings to match your footage, say no.
It looks like you're new here. If you want to get involved, click one of these buttons!