I have an iMac 5K (mid-2017) and a USB-C to HDMI adapter. I used to have a standard 24" monitor (1920x1080) connected to the adapter, and it worked just fine; however, I have put a video capture device in between and while this device supports a 1080p resolution, macOS keeps on detecting it as running at 720p as its native resolution.

I am able to force macOS to run this external device at 1080p by selecting the "scaled" video modes (and it appears to output a correct 1080p signal); however, every time macOS has a video configuration change (from me e.g. switching between mirroring and extending the desktop), it always defaults back to 720p.

Essentially, it always defaults to "best for display," but thinks that this best setting is 720p rather than my preference of 1080p.

Is there any way to force macOS to change its default resolution for an external device, so I don't have to manually change the resolution every time?

  • Have you asked this of the tech support folks for this device? Also adding the make and model of this "video capture device" might be helpful. Apr 21, 2019 at 0:35
  • It's a generic capture device from a generic Chinese brand.
    – fluffy
    Apr 21, 2019 at 6:46

1 Answer 1


It turns out this is one of the many things that SwitchResX can do.

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