Choppy video when playing MOV file in QuickTime Player X

[Part24]

I'm working on a Mac Mini late 2012. The video while playing a MOV file in QuickTime X is choppy but the sound is OK. VLC Media Player plays the file OK. Youtube works OK. The issue is just that any video played in QuickTime has choppy video. We'd just use a different program if that were an option but we need QuickTime to work like it is supposed to.

Info about the file:
File Kind: QuickTime movie
Format: MPEG-4
Size: 23.2 MB
Duration: 00:00:22 (8 805 kb/s)
Video: HVEC, 1920x1080, 30.000 fps, 8 544 kb/s - Core Media Video
Audio: AAC, 192 kb/s VBR, 44.1 kHz, Stereo - Core Media Audio

There is another identical Mac Mini which I've used to play the file and it plays OK. I've been trying to figure out what is messed up on the Mac Mini that has trouble playing the file. After trying for a while I gave up and reinstalled macOS, choosing the option to preserve personal files and settings, however QuickTime Player still has choppy video. I suspect there is a codec lingering somewhere, possibly installed by something else, that is causing problems but I don't know how to find and remove the codec.

 

[Part24]

So, I did a fresh install of Catalina 10.15.7 and found I still had the choppy video problem! The other Mac Mini didn't have this problem and it was still on Mojave 10.14.6. After Googling about the Intel HD 4000 graphics in this late 2012 Mac Mini it seems there are a number of issues with the Intel HD 4000 in Catalina. Basically it looks like Apple broke something related to the graphics and Apple isn't going to fix it. I gave up trying to fix it and did a fresh install of Mojave on the Mac Mini that was having problems and used Migration Assistant to import stuff from a Time Machine backup made in Catalina. It imported some programs that only run in Catalina but I'm sorting that out. The videos are playing smoothly like they should, now, plus I've noticed the Mac Mini is running a bit cooler, too.