Using airdrop sucks for big 4K files from an iphone to a mac (it freezes on big files)! Also using itunes sucks to get video files to your computer.
Here's the best way to download/upload transfer your video files from your phone to your mac.
Connect a lightning to usb cable and plug it into your mac.
Open photos on your mac by going to launchpad.
Select the video files on your iphone and import.
Depending on size it'll take a little bit to transfer but it's the fastest way and you can bypass airdrop. Hopefully this will save someone some grief trying to get their files from an iphone to their mac computer.