When does GPS get written into the .MOV file

How do GPS lat and lon get written to .MOV files on iPhones? Is it programmed to export the coordinates as soon as you press record, when you press end, some other time?

If you are recording and walking or driving what location will the GPS affix to the file? I thank you all so much for your time and help.

It appears that this is the file that the location gets written to? com.apple.quicktime.location.ISO6709