I've been having this issue with my iMac for a long time, over multiple OS versions.
When playing videos with Quicktime (either in the app or, more often, using Quick Look), my system will temporarily freeze. After a few seconds, it unfreezes, but all video files turn completely green.
Interestingly, it affects videos differently depending on playback...
- All videos played in Quicktime or with Quick Look are completely green
- Videos play fine using VLC
- Videos play fine inside Premiere Pro, but are completely green upon Exporting
- Some but not all videos play completely Green on YouTube
Restarting my system temporarily fixes the problem, but it inevitably happens again.
I've tried reseting NVRAM and SMC but that didn't fix it. There are various posts on various threads going back years related to this issue, but I've never seen a definitive answer as to what causes it or how to fix it.