This is the official response I get from the support team at HitFilm.
That could very well be the problem. HitFilm does not support Quicktime Alternative. Please install the correct version of Quicktime, and then let me know if you still have issu…
This was the best solution I got.
Transcode the .mp4 video file into DNxHD codec (for up to 1080p 60fps) or DNxHR (for up to UHD or 4K). For more information, see this thread. https://hitfilm.com/forum/discussion/comment/88026/#Comment_88026
I'd installed the QuickTime Alternative 1.81 and launch MPEG Streamclip 1.2 on my Windows 10 PC. After that I installed the AVID codec (that Triem23 linked) I relaunch the application, but the avid coded wasn't listed. What's wrong actually?