iphone 7 movies do not play on Mac.

I can not view movies created on iPhone7 on Mac. QT 10.4, OSX El Capitan v 10.11.6

Suggestions?

Check your iPhone 7 iOS version. If running iOS v11, then check your camera record settings. If they are defaulted to a format that is not compatible with your current macOS, you can either change the recording mode to one that is compatible with your macOS or go to the Photos settings and reset your iPhone 7 to automatically transfer your files in a compatible format rather than their original format. (I.e., your iPhone 7 operating under iOS v11 now has video and photo formats that are only compatible with macOS High Sierra. My guess is that this is your current issue.)