(In response to:) Videos play MUCH too fast in Safari and Quicktime... see video sample here

Here's a solution that doesn't require a reboot:

https://9to5mac.com/2019/07/29/macos-fast-video-playback-bug-fix-coreaudiod-video/

"Fixing the fast video playback bug

Before doing anything, be sure to save any work that you have open.

To fix this issue, open Activity Monitor and under the CPU tab find the coreaudiod process. Click the ‘X’ button in the upper left-hand corner, and select Force Quit. This will kill coreaudiod, but it should restart immediately.

Killing coreaudiod

Once coreaudiod restarts, it will reappear under the CPU tab. Afterward, close Activity Monitor, and try to play back a video. If fixed, video playback should go back to normal with sound and with standard 1x playback speed.

A restart will fix the issue as well, but restarts take a lot more time than simply restarting the core audio daemon via Activity Monitor. …"