Hi,
Since you have VLC, try using it to convert one of the video clips and see if the converted clip will play in QTP and iMovie.
VLC, File/Convert Stream. Choose Profile Video-H.264 + mp3 (mp4). Convert and Save to desktop.
You can also use the free download, Handbrake, to do the conversion to Mp4/ACC, that Handbrake will do by default. You can get Handbrake here:
https://handbrake.fr/
A simple way to do it is to open Handbrake and do a File/Open Source. Navigate to your video and choose it as the source from the resulting screen. Then do File/Start Encoding. Wait a couple of minutes for the conversion to
complete. Then save and import the converted clip into iMovie.
-- Rich