quicktime player 7 black screen

I shot video on iphone X with IOS 11.3.1 I exported the video to Mac Pro running 10.13.4 High Sierra. I open the file using Quicktime Player 7. The screen is black. The video plays fine in the version of Quicktime Player that is standard on the Mac. My problem is with Quicktime Player 7. The license is up to date and registered.

What is the video compression format of the file transferred to the Mac Pro—AVC (H.264) or HEVC (H.265)? The QTX player app supports HEVC playback under High Sierra but the "legacy" QT7 media player does not.

This is moot. I decided to keep using quicktime x since it appears to function well

Not so moot if at some point you decide you need continuing compatibility with older macOS, iOS, and/or tvOS devices/apps or family/friends using such devices/apps. (I.e., you can reset your iPhone X to record AVC videos or continue to record HEVC videos but transfer the HEVC files using the AVC video compression format or you can choose to convert files from HEVC to AVC on a file by file basis—whichever option best suits your workflow needs.)