I don't remember installing anything new, but there's a process called replayd that is constantly consuming over 90% of the CPU. If I kill it, it comes back immediately.
My investigation shows the culprit might be Slack. After closing the app, this process ended.
What could it be?
replayd is a MacOS daemon to support screen recording and video capture.
Don't forget that the %CPU reported in Activity Monitor for each process is per core. So if you have an 8-core CPU, 90% is 11.25% of your total CPU.
I had this issue in a different way, which I will describe (with solution) in case it helps someone.
The short version: Try revoking the Screen and System Audio Recording permission from from as many applications as possible, because it seems different applications, and even different instances of one application, can have some kind of contention gaining access to replayd, even when there is no screen sharing or recording going on.
I run Chrome on macOS, usually with two or three profiles open across multiple desktops, usually without any problems. But then, because I am a developer with some quite specific needs, I began starting Chrome in a separate process, so that I actually had two Google Chrome icons in my dock. As soon as I did this, the replayd process would shoot up in CPU usage, and my system temperature would start climbing towards >95°C. I first noticed there was a problem through my fingers getting hot when I reached for the function keys! This is on a MacBook Air M1. The replayd process came to my attention simply because it appeared at the top of the list in Activity Monitor when I ordered the table by the % CPU column.
But why would Chrome be using replayd, which is a process that is part of the built in macOS facility/library, ReplayKit (see https://developer.apple.com/documentation/replaykit)? I figured it must be something to do with the fact that I often share my screen during Google Meet meetings. I decided to revoke Chrome's permission to record the screen (even though I definitely was not doing any screen recording or sharing while having this problem). That permission is granted (and revoked) under System Settings / Privacy and Security / Screen and System Audio Recording.
With that permission revoked, replayd has once again become a well-behaved background process using a reported 0.0% CPU (I am monitoring it in Activity Monitor), my system temperature is back at around 45°C, and I am able to use Chrome in a separate process for my slightly arcane developer purposes.
I will have to specifically enable Screen and System Audio Recording again when I want to share my screen, and disable it afterwards, but that's okay.
I think the problem here was/is some kind of resource contention between the two instances of Chrome, both claiming permission to record the screen — some sort of back-and-forth, in which each one immediately reacted to the other one, endlessly.
My case, with two instances of Chrome, is quite unusual, but if you find replayd using a lot of CPU, I would suggest checking which applications have the Screen and System Audio Recording permission and revoking permission from as many as possible (ideally all) to see whether it makes a difference.
I notice there is also a System Audio Recording Only section in the permissions dialog. I haven't experimented with that.
Hardware Overview:
Model Name: MacBook Air
Model Identifier: MacBookAir10,1
Model Number: Z125000L5X/A
Chip: Apple M1
Total Number of Cores: 8 (4 performance and 4 efficiency)
Memory: 16 GB
System Firmware Version: 10151.120.115.0.4
OS Loader Version: 10151.120.115.0.4
Activation Lock Status: Enabled
System Software Overview:
System Version: macOS 14.5 (23F5049f)
Kernel Version: Darwin 23.5.0
Boot Volume: Macintosh HD
Boot Mode: Normal
Secure Virtual Memory: Enabled
System Integrity Protection: Enabled
Google Chrome:
Version 123.0.6312.124 (Official Build) (arm64)
For me, restarting discord fix the issue
