I am running a Pi4 with 2GB of ram. SD card for OS. Emby server + nas for data storage, Pi4 is mounted in a Flirc all aluminum case. No fan.
I was having a display freeze problem when I used fast forward during video playback. The whole display would lock up but I could still access the system with SSH. Still required a reboot to get control through the user interface.
I turned off Allow Hardware acceleration MMAL and then fast forwarding worked just fine.
While using fast forward debug is on. I see CPU usage on one of the CPU's runs at 100% while the other 3 are in the teens or lower. After some seconds the high activity moves to a different CPU. I suppose this is happening to manage heat dissipation.
stepping through replay speeds (1x,2x...32x) on the 1080p video I see a range of cputemp readings from 40c to 46c.
All this is really great. I can't imagine that I would see a better heat profile even if MMAL worked so I will leave hardware acceleration off.