Since Macs don't have an HDMI input, HDMI sources must be connecting using an additional piece of hardware called an HDMI encoder or capture device.
Popular HDMI capture devices include Elgato's Cam Link 4K, and Blackmagic Design's UltraStudio Mini Recorder.
These devices accept an HDMI connection, and connect to the Mac. Once connected, the camera can then be used with Ecamm Live.
Choosing an Encoder
For older Macs that have a Thunderbolt connector, but not USB 3.0, we recommend Blackmagic Design's UltraStudio Mini Recorder. You can learn more about connecting a Mini Recorder in this step-by-step tutorial video.
For newer Macs that have USB 3.0, we recommend a USB-based encoder. Here are a few that we like:
Elgato's Cam Link 4K: This is a great option because it's affordable and supports 4K video resolution. (Currently sold out.)
Elgato's Game Capture HD60S+: Another great option from Elgato. Make sure you get the S+, rather than the S. Appears to still be available on Elgato's website.
Magewell USB Capture Gen 2: A popular option, also compatible with USB 2.0.
With the exception of the Blackmagic Design device, HDMI encoders are plug-and-play, as they present as a webcam on the Mac, and will show up automatically in Ecamm Live.
Checking for Clean HDMI
When using a DSLR camera or camcorder's HDMI connection for live streaming, you'll need to ensure that the camera provides "clean HDMI". This means an HDMI signal that doesn't contain the on-screen information, focus rings, etc. that can be seen though the camera's viewfinder. To check this, connect the camera's HDMI cable to an encoder, or to a television or display and ensure that you don't see any on-screen text on the video feed.
Some cameras have a setting to turn on a clean HDMI mode, some provide clean HDMI all the time, and some cameras do not have the ability to provide clean HDMI.
Ensure That The Encoder Supports Your Camera's Resolution and Frame Rate
Each HDMI encoder supports a range of video resolutions and frame rates. For example some encoders may not support 1080p60, while others support up to 4K resolution. Before purchasing an HDMI encoder, ensure that your camera can provide an HDMI resolution and frame rate listed in the encoder's technical specifications.
Digital Trends in depth article How to Use (Almost) Any Camera as a Webcam by Hillary K. Grigoins, has a ton of helpful ideas and thorough explanations of how to accomplish them. We recommend the read.
If the HDMI encoder isn't providing video to Ecamm Live, review these troubleshooting steps.