when I play html5 videos in my fresh Antergos system it is just a matter of seconds until the mouse pointer freezes and all input is ignored until the system does a hard reboot.
I had the same issue in linux mint but changed graphics card and ssd and ram in the meantime. Also stress tested the system so I’m pretty sure it is not hardware-related.
Using nvidia proprietary drivers for gtx 970 and intel 4790, 64bit system.
Glad if you have ideas!