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Today I learned something again. My MacBook Pro suddenly became quite slow, keystrokes took seconds and the mouse pointer only moved in slow motion. A look at the "Activity Monitor" utility - permanently installed in macOS and found under "Applications" -> "Utilities" - immediately showed me the cause: A process called "VTDecoderXPCService" has the CPU properly besieged and almost continuously over 100% of the Computing time drawn.
A quick research on the Apple Support forums showed me that I seemingly not the only one am where the process surfaced. Apple's rationale is as follows:
The VTDecoderXPCService process is responsible for all sorts of things related to Quicktime. It "sandboxed" these processes and ensures that they cannot access unwanted memory areas. So if it's anyhow about audio or video playback, then the process on macOS Sierra should be involved.
In my case it was almost clear to me what kind of program was responsible for this, because further down I found the process "com.apple.photos.VideoConversionService" and this - so my assumption - calculates the videos from my photo library. to upload them to iCloud. I closed "Photos" as a test and the Mac was running again without snail mode.
However, according to the Apple support forums, a webcam, video display, or something similar can also call up the process. So you should think about what is running on your Mac, what may have called this process. Ending programs at intervals helps to determine which program may be responsible. You can see which programs are all running when you press "cmd" + Tab on the keyboard.
If you are wondering what the top process called "kernel_task" in the screenshot is doing, which also generates over 100% CPU load here: This process intervenes when the Mac's CPU gets too hot. Then the processes are interrupted and only processed in parts so that the CPU can cool down. The result is that the Mac is slowed down a lot. If you provide better ventilation and cooling, the CPU load of the kernel_task process drops again.
In order to keep an eye on the CPU load and the temperature of the CPU, I can recommend the "iStat Menus" program. With this you can show a small graph and the current temperature of the CPU in the menu bar, which is very practical.
Jens has been running the blog since 2012. He appears as Sir Apfelot for his readers and helps them with problems of a technical nature. In his free time he drives electric unicycles, takes photos (preferably with his iPhone, of course), climbs around in the Hessian mountains or hikes with the family. His articles deal with Apple products, news from the world of drones or solutions for current bugs.