An iMac has a large, sharp display built into it. It seems obvious that you should be able to connect another device and use the iMac like a normal monitor.
But on modern iMacs, that does not work. The USB-C, Thunderbolt and Mini DisplayPort connections are not general-purpose video inputs. Connecting an HDMI adapter in the opposite direction will not make an external device appear on the iMac screen.
There is, however, a simple way around that limitation: use an HDMI capture device and display its live video feed on the iMac.
What You Need
The setup consists of three parts:
- An iMac that can run AV Monitor Pro
- A USB HDMI capture device compatible with macOS
- An HDMI cable from the source device to the capture device
The connection looks like this:
HDMI device → HDMI capture device → USB → iMac
The capture device converts the HDMI signal into a USB video source. macOS can then treat it much like an external camera, while AV Monitor Pro displays the feed in a clean monitor window or fullscreen.
What Can You Connect?
Almost any device with a standard HDMI output can be used as the source, including:
- A Mac mini or another computer
- A camera
- A game console
- A set-top box or media player
- A single-board computer
- A video receiver or other HDMI equipment
This can give an older iMac a useful second life instead of leaving its display unused.
Why a Cable Alone Does Not Work
Some older iMacs supported a feature called Target Display Mode. It allowed selected iMac models to display the screen of another compatible Mac through Mini DisplayPort or Thunderbolt.
Unfortunately, it was never a universal HDMI input. Apple’s current requirements restrict it to specific iMacs introduced between 2009 and mid-2014, older macOS versions and a connecting Mac from 2019 or earlier. It also does not support Windows through Boot Camp.
For most current setups, Target Display Mode is therefore no longer a practical option.
An HDMI capture device works differently. It presents the incoming signal to macOS as a video source, so it is not dependent on the old Target Display Mode feature.
Using AV Monitor Pro
AV Monitor Pro is designed for exactly this kind of setup. It provides a focused live view without the controls and complexity of broadcasting or production software.
To start monitoring:
- Connect the source device to the capture device with HDMI.
- Connect the capture device to the iMac by USB.
- Open AV Monitor Pro.
- Select the capture device as the video input.
- Select its audio input if you also want to hear the HDMI audio.
- Switch to fullscreen if you want the iMac to feel like a dedicated monitor.
AV Monitor Pro includes separate video and audio source selection, a live audio level meter and optional H.264 recording to a .mov file.
There is no subscription or account requirement.
Is It the Same as a Real Monitor?
Not quite.
A capture device must process the incoming signal before the iMac can display it, so there will always be some latency. How much depends primarily on the capture hardware, the selected resolution and frame rate, and the source device.
For camera monitoring, checking another computer, configuring a headless device or watching ordinary video, a good low-latency capture device can work very well.
For competitive gaming or other situations where every millisecond matters, a direct hardware monitor remains the better choice.
Also check the maximum resolution and refresh rate supported by the capture device. A device advertised with “4K input” may still deliver only 1080p over USB.
A Useful Second Life for an iMac
The iMac may not include a conventional HDMI input, but its screen does not have to remain limited to the iMac itself.
With a small USB capture device and AV Monitor Pro, an iMac can become a clean live monitor for computers, cameras, consoles and other HDMI sources — without relying on an obsolete display mode or setting up a complex streaming application.
Learn more about AV Monitor Pro or download it from the Mac App Store.
