How to capture from HDMI with Ubuntu?

For anyone coming to this page from Google:

For EDITING video: To capture HDMI content in Ubuntu, you can use HDMI capture USB boxes (such as Magewell XI100DUSB-HDMI) or HDMI PCI cards (such as Blackmagic Intensity Pro).

Also, you may need to use a Linux-centric video solution such as ShotCut if you want these cards to work well.

For LIVE STREAMING video: The above-mentioned cards might work but will require gstreamer in-between to make the Intensity Pro's inputs available in V4L(2).

Also, please note that for any of this to work, your video has to come out in unprotected mode (non-HDCP), otherwise your capturing won't show any video/audio.

I'd like to add another V4L2-compatible device to the list since this page is very popular on Google: the Avermedia LiveGamerPortable2.

I tested it on Ubuntu 16.04 with OBS and works perfectly out of the box via USB in both its "PC" mode and "external storage" mode.
Avermedia doesn't officially support Linux but the "uvcvideo" module does the job flawlessly.

If you want to record HDCP protected content, there is hardware available that can strip this before you input into your capture card. For instance there is a SCART to HDMI converter that also has an HDMI input that passes through without HDCP.