It seems the source is interlaced, means it has 60 fields per sec, which naturally converts into 30 frames per second.
I'm bumping this comment to the main thread. What I wrote here about "Just to add a little clarification" has been moved to the main thread.
Just to add a little clarification: There's no conversion from 60 fields per second to 30 frames per second. They're two different ways for referring to picture that's interlace scan.
It certainly doesn't help that the abbreviation "fps" is for both frames per second and fields per second.
It's also probably one of the more confusing things about working with interlaced video that 1080i60, 1080i30, 1080i59.94, or 1080i29.97 are each correct ways to summarize settings for the same file.
Of course, this is not to be confused with de-interlacing i60 to p30 in which case there is a conversion.
Actually, this may be a better answer:
You're recording your video at i29.97 (also called i59.94). If you want p60, check to see if the device that you're using for recording supports p60.
An "i" inidicates interlaced scan which is commonly used when recording from or for broadcast or cable.
A "p" indicates progressive scan which is commonly used when recording for desktop video or web video.
Thanks everyone! I didn't know what to do with my problem, you helped a lot!