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Whenever I connect my Intel MacBook Pro to an external 4K-display and playback video on YouTube or on a video call, for example, CPU usage on kernel_task gradually increases until all 8 cores are at almost 100% and the whole system slows down. The video becomes choppy and I am forced to terminate whatever video-playback is running or disconnect the external display.

This seems to be independent of the video resolution of what I am playing.

The only difference seems to be that when I connect my external display, the graphics changes to use the AMD-chip, when I disconnect the display it falls back to the Intel-chip.

So when using the more powerful graphics-chip the video playback capabilities are worse than when using the less powerful one.

Is there anybody with the same problem? Is there any way to fix this behaviour?

2019 Intel MacBook Pro 16"

  • Graphics: AMD Radeon Pro 5500M 8GB and Intel UHD Graphics 630 1536 MB
  • RAM: 32GB
  • CPU: 2,3 GHz 8-Core Intel Core i9

Details

  • Connected via USB-C to a display that also charges the Mac.
  • Mac is not in low-power mode.
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  • @Allan explained in a similar question a few days ago (see apple.stackexchange.com/a/471534/362111). Now that doesn't exactly explain why your MacBook Pro has its CPU/GPU throttling its performance, but it does explain how the GPU is used for the external monitor. Also, have you tried reducing the refresh rate to 60Hz or lower instead of 120Hz? That could help. The only other thing I can think of, is that the large amount of data that your Mac needs to send/receive to produce 4k videos could also be putting a large strain on your CPU usage. Commented Apr 5, 2024 at 15:17
  • The Refresh rate is at 60Hz. There is no higher option to choose from in my Settings -> Display. The videos I am playing are not 4k videos. I get the same problem with 480p and 1080p videos playing. I can see the load increasing over time in Activity Monitor. Playing back video should'nt get more demanding the further you go into the video right? Commented Apr 5, 2024 at 19:10
  • I don't know TBH, though googling your issue, I found that some users report that using a USB-C monitor uses less power than using an adapter to convert your MacBook's USB-C output to HDMI, so are you using an adapter to connect your display? Also someone suggested check if your battery settings are set to low power mode. I know this sounds counterintuitive (since your Mac is plugged in presumably?), but disabling low power mode might fix the CPU throttling(?). Also are you using Chrome, because it is extremely resource intensive on macOS. Finally, have you tried resetting the SMC? Commented Apr 6, 2024 at 3:29
  • Should also add, some applications will have settings to disable hardware acceleration like Classic Microsoft Teams. For web browsers, usually these options are hidden in advanced settings/developer menus. This might help. BTW, resetting the SMC or changing any of the power/battery settings in system preferences will recompile the plist associated with power management, which might help squash out any corrupt settings associated with power management. So you may want to try enabling/disabling some of those settings and see if there's any improvement. Commented Apr 6, 2024 at 3:43
  • Resetting the SMC did not help. What makes you think the CPU throttles? I closed all other applications except the one doing the video playback. I have had this problem with zoom (running as the only application and viewing other peoples webcam) and also with firefox playing a youtube video with low quality. Commented Apr 15, 2024 at 17:34

1 Answer 1

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I am also on the same setup (UBC-C Charges the Mac and gives out display to the monitor).

If you want to play it on Google Chrome effectively:

  1. Open Chrome, select the three dots on the left, then select Settings > System (left hand side, bottom).
  2. Turn on "Use graphics acceleration when available".

After these changes the video should work fine.

If you want to play it on Safari, Apple has updated Safari and it's already fixed.

Make sure your Mac is not in power saving mode (I know you have mentioned already).

Last attempt if nothing else helps: Reduce the monitor frame rate to 60 Hz.

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