View HDMI output from another device on a Mid-2015 MacBook Pro I'm looking for a setup that will allow me to view the video output from another device (1080p/60 over HDMI) on my MacBook, at full frame rate and with minimal latency. I assume this would take the form of a Thunderbolt dongle, but I don't know what to look for, or if such a thing even exists.

I don't need to be able to capture or encode video, though being able to save frames would be a plus. I'd also like to be able to view the video output scaled to full-screen, and if there's the option of software filtering (e.g. sharpening / fancy upscaling), that would be a plus as well.
You can use a device such as the Elgato HD60 S, which offers low-latency capture from a 1080p60 HDMI source, which you can view on your MacBook over a USB 3.0 connection. 

It also allows you to save and stream the video if you want to do that as well.

It's available from for example Amazon at $179.95:

https://www.amazon.com/Elgato-Game-Capture-HD60-technology/dp/B01DRWCOGA