With iOS 11, Apple adds a looping feature for Live Photos. Snapchat and Instagram have similar possibilities. However, videos on the Mac can also easily play as an endless loop. Apple provides the appropriate function in the popular QuickTime Player ready. No foreknowledge is required and works in a few simple steps.
How to Loop a Video Loop with QuickTime
Open the Finder and open the Applications folder. Then select the QuickTime Player application in it. After that you will see a window where you can select the desired video. Once you've selected a video, click "Open." Start the video by clicking on the start button.
Now select in the menu bar at the top of the screen the entry "Appearance" and then click on the item "Infinite loop". Alternatively, you can also press the following key combination: Option key (alt) + Command key (cmd) + (L). The video will now run until you stop it again.
Tip: The effect is particularly useful for time-lapse photography. If you adjust the tempo, it will be kept throughout the playback.