I'm using a Mac mini (late 2012) with Mojave 10.14, and I'm having issues with video playback.
After using the Mac to play back videos, whether that's online streaming/YouTube or IINA/VLC video files playback - after about 8-10 minutes of use it freezes for a few seconds, than continues without any issues for another 8-10 minutes, freezes again, and so on.
The same behavior is observed while playing videos from internal HDD or DASD.
Needless to say, it was perfectly fine under High Sierra (same apps, and content).
I use Internet cable connection (up to 150 Mbps download speed, and up to 15 Mbps upload speed) exclusively, WiFi is OFF. Hardware configuration: RAM: 2 x 8 GB DDR3 1600 MHz GPU: Intel HD Graphics 4000 - VRAM: 1536 MB Display: HP ZR30w 2560 x 1600 Resource usage while playing video: RAM: Physical memory 16.00 GB Memory used 8.71 GB Cashed files 7.28 GB Swap used 1.96 GB CPU: System: 2.27% User: 3.94% Idle: 93.99%