There are a few extra pins you will see in a HDMI connector pinout. These are way more fun than you might know of, and I’m not even talking about the I2C as some might guess. For a start ...

The first is the mini-HDMI, or Type-C. This is about half the size but still has all the 19 pins, though some of them have their uses swapped. It’s seen on the side of DSLRs and mirrorless cameras.